I have a question...I´m selling a 1979 Suzuki GS 750, but the bike got dumped in my driveway overnight by some hooligan. What looks like oil leaked out all over the driveway. I don´t see any crack in the case or anything, any ideas of where it could have leaked out from? Also, I´d like to put new oil in, but would like to make sure all the old is out. Where is the drain screw? Thanks!