Just filled mine with Royal Purple 75w90 GL-4 from Napa Autoparts. The MT-90 was a little more expensive and difficult to find. The only store I found that stocked it only had 2 Quarts.

If you are doing it yourself, make sure to get yourself a pump of somekind to pump the stuff into the fill hole. You can't get to it with the bottle alone.

Edit to add: My tranny now shifts like the day it was made. I guess leaving it to 80k miles probably wasn't the wisest idea! The stuff that came out was pretty black, but only a few small iron filings on the drain plug magnet, so don't think there is any damage in there. I'm planning on changing it again in another 10k miles, to flush out the rest of the old dirty stuff.