Many have had good luck with ATF TYPE F in their trannys. its cheap enough so it can be changed after every ride. I use atf type f and sometimes use castrol gtx 10/40 and sometime use motul 2 stroke tranny oil...whatever I have on hand.
I run maxmia 80wt for mx and 85wt when i race cross country. I recomond running oil that is desinged for a 2stroke gearbox I have seen a few clutches burrned up from people using motor oil in their tranny.
Thanks for all the replys.I am presently trying 10w40 in the last week and its cheap and
seems to be doing ok.Thanks again for all the responses.We also have a ktm and I wonder
if we could run 10 w 40 in it to save some money over 7 bucks a quart belray.I will post
over in ktm section also.Thanks for all the help.