IIRC, it's near the exhaust where it bolts up to the head. That's what makes me think the head is cracked. I have a huge TIG welder, so I could repair it, but I just haven't dug into it. Got tired of tearing into that engine. I had it torn down some 4 or more times.
I rebuilt the engine, then the tranny lost a fork, so I tore it down again, then I did that cam chain mod and it ended up dropping a valve, so I rebuilt it again and went for a ride, when I stopped to eat, there was a puddle of oil.
The carbs where torn down several times and bought a jet kit w/K&N then they started screwing up, as if they were flooding and I kept cleaning them out and replaced the needles but still no luck.
I kept working on it because I have a parts bike, so I got lucky with spare parts, but I don't have any more heads.
Gave up on it and started searching for the 919.
It's sad because it has some nice parts: corbin seat, engine guards, jet kit, K&N, new friction and steels, and all the other parts are nice shape. The frame was sandblasted, rust prepped and painted.
She was running good before the valve dropped, I could notice the effects of the jet kit and K&N.