I'd get some cheap ass oil at first and run it for a little bit with that in it. by a little bit I mean as it sits in the stand and you tinker with it getting it fine tuned and whatnot. Drain that shit ALL out and let it take whatever built up whit is in it out. Using one of these new high milage oils as a refil may not be a bad idea either. they claim to have a additive in there than rejuvinates all of the internal soft parts. The marvels mystery oil may do the same thing. a bunch of the older cats swore by that shit at one time. I have started adding a little Lucas to mine and it really does seem to make it run cooler and quieter. You never know though, you may get it running like a swiss watch and every gasket on the fucker be dried out and it leak like a screendoor on a submarine. You just dont know till ya do it.

Hell, there is no telling what's in there. Engine gunk, mice, wasp, small people...fuck, no telling.

I guess maybe another concern would just be sludge/gunk built up from old oil. They sell engine clean out shit, not sure what it is really called, or you may be able to use B-12 Chemtool to cycle through there. I used some of that engine crap in an old truck once and it did pretty good. You pour it in and run it at idle for a few minutes and drain everything out, refilling it with fresh oil. It claims to wash out the inside of the crankcase and shit. Never used it on a bike....so...that's up to you unless others speak up.