I've changed my 020 gearbox oil to Castrol SMX-S 75w-85. Made a huge improvement on gear change I recommend it to others. I know people recommend MTL or MT90. I thought I'd try something different. Bought another batch to change my 02a box lets see if this box has any improvements.
well the oil comes out so dirty, the rest of the box will probably have a coating of the dirty stuff, hence it would be nice to flush it out. not sure if ATF would harm it though id probably flush it with cheap box fluid then put your nice stuff in
You could buy some flushing agent (can`t remember who sells it). Basically, drain the box and re-fill with new oil with 10% of the volume (so about 200ml) being flushing agent, drive round the block a couple of times (10 mins or so) then do a full change again. Same principle can be used on the engine. Does a cracking job of getting rid of oily deposits...if you can find some! I think this is the theory behind using ATF in the engine. Shouldn`t be problem using it in the gearbox aswell.
ATF used to be one of the 'trick' mods for a really slick change in RWD Ford gearboxes years ago Not sure whether it will be adequate for continued use in a FWD final drive though, I rather doubt it. You could maybe do a short distance flush with ATF before the Redline
