Had a similar issue with mine, and it ended up being a failure of the seal between the case halves at the back of the crankcase/front of transmission. I wouldn't ride it, or start it anymore, until you find the leak, and get it fixed. I got lucky, and didn't tear up stuff, but that was very unlikely occurrence. Your chances of tearing up a bunch of shit, and costing you big money are really high, if you keep on riding it/starting it without finding out what's wrong, and getting it fixed.