I'll go for the last one first :
https://www.ebay.co.uk/itm/Carlube-A...e/233257297843
Next, like Forrest says, garages tend to run away from changing gearbox oil, especially autos as they don't really understand them. Sadly because of that, they often give incorrect advice as they have this time!
If using the "flushing method" as described by Forrest, it should be done every 24k miles or 2 years.
However, i favour the "part-change" or "sump-dump" method. Two ways of doing it, one is jack the car up so it's level and remove the drain plug in the transmission sump pan and let the contents flow out into a suitable container, refit the drain plug and refill the box via the dipstick with fesh oil - usually 2.5-3.5L
What is easier is to get the car facing downhill and use a fluid extractor pump.
https://www.ebay.co.uk/itm/Car-12V-6...e/352754565259
Feed the suction pipe all the way down the dipstick tube to the bottom, arrange the discharge (larger bore) into an empty 5L container, connect the clips to the battery then switch on and go and have a cup of tea, coffee or whatever for 20 minutes.
Come back and see how it's doing, should be nearly finished pumping. You'll know when it has as it will start making squelching noises and the fluid will come in fits and starts.
Switch off and discoinnect the clips, remove the suction tube from the dipstick and put the pump, 5L container out of harms way then top up the fluid on level ground to the "COLD" mark on the dipstick with the engine idling in N or P.
Take it for a drive to warm up the fluid and recheck again on level ground, topping up as necessary.
All methods should have the fluid warmed up first by a drive of 5-7 miles, be careful as it will be hot. If using the part-change method, repeat after a month to total 3 or 4 changes, depending how clean the third lot comes out.
Repeat one part-change a year after to keep the fluid clean and fresh.
The big danger with doing the flushing method, especially on an old box, is the "seal swell" in the ATF will have worn off, allowing the seals to dry and become brittle. THis means when a complete load of new fluid that is much thicker goes in, it's all too easy to blow these seals. Doing the 3 or 4 part changes a few weeks apart gives the seal swell in the new fluid time to revive the seals and clean the inside of the box so more and more dirt will be removed each time until it's no longer dirty inside. This also helps clean the filter too as the deteregent effect of the new fluid causes the debris on it to drop off as it's no longer dirty. This gets removed by the pump when you use the extractor pump method.
Glad you've brought this up as it's reminded me i need to get some ATF-U to do the annual change on both of beasties. I use ATF-U as it's Honda Z-1 comatible so is suitable for my other beast and it's also JWS3309 compatible which means it's good for the Toyota A341E box which is pretty much identical to the AW-71 boxes we have in ours.
I have also used it in a ZF4HP22 in an XJ Cherokee i used to own so even if you have a ZF box in yours, you'll know it's ok for that too.
Can also be used as PAS fluid (again, both of mine are using it) and numerous other uses too.
Think i've covered everything there, feel free to ask if not. :thumbs_up;