I wouldn't worry bout the oil in the tank for the little they put in it. I would just dump the tranny oil right off the bat, and wether you run synthetic or regular mineral oil it's no big deal really, just baby it longer if you run synthetic for the first few tanks and vary the RPM's and be sure to shift through the gears pretty good without putty much of a load on the bike, so don't shift too high a gear and lug it everywhere. You'll do more damage lugging it than letting it come up on revs for a short bit. On a 4 stroke, I would dump the motor oil right away and put synthetic in the cases, right from day one. I would run any motorcycle oil, but preferably an oil that suits the bike the most, there are oils more designed for premix or injected specifically. Same with synthetics setup for 4 stroke wet clutches. Just read the bottles well and ask around at the dealerships what they recommend.