The back plate housing could be lose and/or the gasket is bad? Could be leaking from the front of the crank?
I'll check/clean/RTV the back plate while I'm at it, although I would think that would cause the engine to run poorly in general.
This is a really nice little motor...don't booger it up.
Of this, I am aware. Runs great, good power and awesome RPM, although it does vibrate quite a bit.
Thanks, all,
Phil