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With pictures from Edgar, this is advice from Robert G, who has carried out this work on his own autobox.

OIL CONDITION

If the oil is brown or black and smells burnt the box is on its way out and will require new bands at the least and changing the oil is not worth the expense. Otherwise the fluid should be fine for the service life depending on mileage about 80,000 miles town driving and more on motorways. However if the fluid still looks red and does not smell burnt then after several years of usage it would benefit a change and can help in some cases. Some Scorpios are 10 years old!!!
 

PARTS

The first things are to obtain the correct gearbox filter for your box. It is a pan type filter which is not possible to clean and only costs about £10 from a good auto dealer or a little bit more from Ford -  (£12.77).  You will also need a new gasket for the gearbox sump - again about £10. You will also need the little oil o ring seal for the oil filter as this is not supplied with the Ford filter.  Use your VRM or VIN number to ensure you collect the correct parts before you start the work.

FLUID

The next thing to check is if you have the optional gearbox oil cooler fitted (It is a small radiator located below the main radiator at the front of the car)  This is important as it will make a difference to how much gearbox oil you will need - 6 litres or 9 litres approx (With oil cooler). If your model does not have an oil cooler fitted try to fit one as this does prolong the life of the box as they run very hot! The gearbox fluid can be bought from Ford or a good Auto shop. Ford oil costs about £100!!! but at a good Motor Factor it will be about £30.  Check your specification as later models do not use Dextron II but a different oil which is more expensive.

DRAINING
The job takes about 3 hours with a ramp and a bit longer if you have the car on floor ramps. Get the car in the air so that you can get at the bottom of the gearbox.

If you have a suction pump you can drain some the oil out but it is still a messy job - I had a ramp and a proper oil drainer but it was still messy. In my case I disconnected the battery then I disconnected the oil cooler hoses from the gearbox off side of box (You will need a ring spanner with a cut out to undo the hoses: if not an open end spanner will do but it will take longer)

Remove the dip stick. I then undid all the bolts (about 20) holding the gearbox pan on leaving just 2 in place to make sure it did not empty itself all over my head, then I undid the last 2 and angled the pan to one side to empty the oil into the drainer. This can be very messy so stay clear off the box as it will drip on your head as the filter drains. Totally remove the cover and put it to one side to allow the oil to drain out in a tank or bucket!

You will then be able to see inside the box.  The pan type filter is an aluminium pan type held in place by just one bolt (10 mm I think) - remove this bolt and slowly pull the filter off. It will be stiff as it is located onto a tube but it will come free.

Be careful as more oil will dump on you at this stage! When you have the filter off you will see a small O ring fitted to the neck of the filter so be sure to replace this onto your new filter because  if you miss this it will cause problems!  You could re use this O ring but as the cost is small it would be a false economy.

On my box as I was not in a rush I left the sump pan off all night to allow more of the oil to drain but if you do not have this luxury then you can just replace it.
 

REBUILD
To rebuild fit the pan type filter with the new oil ring into the box and replace the bolt and torque up to the correct value. (Be careful as the box is aluminium and the bolt thread could easily be damaged).

Make sure you clean the sump pan up as best as possible and check for signs of metal in the pan bottom as this could mean problems.  Metal filings are from the brake bands, while little gritty black bits are from deteriorated seals. Too much of both indicates that the autobox is reaching the end of its service life.

Remove the old sump gasket and replace it with the new one - I cover the gasket with fluid to help it bed in. Offer up the sump pan to the box and replace the bolts, torque them up. Replace the oil cooler pipes and tighten, this is very difficult as they are a bit awkward.

REFILL

The next bit depends on oil cooler or not! fill the box up with about 4.5 litres or 8 litres (cooler fitted) of the relevant oil through the dip stick hole and check for leaks from the sump. Filling the box is a slow process as the filler neck is very small. Refit the battery. If all is well start the engine. Give it a minute or two to see if oil is leaking and if all is well then put your foot on the brake and engage Reverse then Drive several times.  The shift may be a bit clunky at first as oil circulates but this should go in a few seconds. Make
sure drive is taken up, allow the box to get warm (when engine is up to temp is a good guide) then check the gearbox fluid level. This is done with the car in Park and the engine running and the level should be well up on the marks, about half way up the dipstick with the oil quantities I have suggested.

Take the car for a run, not over-stressing the box but just to allow it to get up to temp and to ensure selection is o.k. - about 2/3 miles is sufficient.. Then return to your garage and check the levels. They will be low but just top them up to just below the full mark as this allows for expansion when hot.  I then check the box on a regular basis and when I have been on a long run and got the box hot, top the oil up to the full mark.

RESULT

Depending on how clogged the fluid filter was and the general condition of the autobox, operation may well be much smoother and quieter. A noticeable decrease in noise from the ATF pump (the whine when moving off) may be achieved. On a 100,000+ mileage car it can restore an as-new performance and is recommended by several owners.

Note
When you first start the engine it will run a bit erratically as the engine management system relearns its values. You will lose your radio code and things like the window one touch will need re setting!!!!

Some engagement problems and change noise could be due to band adjustment.

Other gearbox problems can be due to electrical gremlins like looms and MAF sensors.

ANOTHER FLUSHING METHOD

From Norway, Terje G suggests a method of flushing the old fluid out of the torque converter too - (this would normally remain in the TC and mix with the new fluid after the change.) He wrote to us on the List:-

My procedure is as follows:-

Prior to change of filter

Disconnect one oilpipe to radiator, put something under to collect oil, start engine and allow idling until approx one litre has poured out.
Stop engine and fill one fresh/new litre of gear oil.
Repeat until approx 5 litres have been changed this way.
Connect oilpipe to radiator.
Change Autobox filter, allow an hour or so to drain prior re-assembling.

After change of filter.
Fill up with approx 8 litre fresh / new gear oil.
Start engine and check level.
Fill to correct level.
Disconnect again one oilpipe to radiator, put something under to collect oil.
Start engine and allow idling until approx one litre have poured out.
Stop engine and fill one fresh/new litre of gear oil.
Repeat until approx 5 litres have been changed this way.
Connect oilpipe to radiator.

Will cost you 10 litres of new oil, however much less if done by a specialist shop - at least in Norway - (Autobox oil cost is approx 5 Euro per litre; hourly cost at specialist shop is 90 Euro)
 

Pix by Edgar. Words from Robert G and more from Terje G.  Thanks guys!