one time we were out cuttiing wood in the middle of nowhere and ran out of chain oil .. all there was in the truck was some ATF and figured what the hell.. But after about a minute the chain and bar was burned .. chain sprocket stuck pretty good, too.
So what's in that tranny? Unless you put something in, you really can't say .. and maybe the last guy put in the wrong stuff.
"THIS":http://www.mopedriders.org/article_view.php?faq=2&fldAuto=17 jawa manual says use 30wt motor oil in the tranny.. If i had doubts, I'd flush whatever's there with kerosene or similar and refill, run and drain it a couple times.. maybe alls it needs is fresh, clean lube.