Just finished a complete engine rebuild of my 75 R90 with 120k miles. Runs great, and I've put about 50 miles on the new engine. However, I noticed quite a bit of oil coming from flywheel area.. enough that I needed to pull the tranny to see if it was rear main or oil pump cover (both renewed when I rebuilt the engine). .. I DID block the crank, by the way :-)

Well, the flywheel came off without a hitch. Oil pump cover did not appear to be leaking, but I replaced the o-ring anyway. Back of flywheel was wet with oil. Oil seal looked fine. I looked at the flywheel sealing surface and it's ok.. nothing to snag a fingernail. no ridges.

I reinstalled the flywheel today, and just to be sure, left the tranny off and installed carbs and tank so I could start the engine while watching the flywheel.

Sure enough, leak is still there. Nothing coming from the oil pump cover. Oil is being slung around behind the flywheel.. It must be the seal.

I checked the crankcase vaccuum by loosening the dip stick .. it's fine. The check valve is doing its job.

This is the new teflon seal, installed after soaking overnight in 10w30, by the book, with the installation tool. It's square to the case, about 1mm proud.

So.. I'm a bit frustrated. I hate the thought of replacing the seal only to have it leak again.

Is it possible that this new seal will begin to work after a time? It's currently leaking about a pint every 100 miles.. enough to leave a large puddle wherever I go, and it's coating the rear wheel. Not a good thing. Could it be leaking somewhere else?

I'm also thinking of going back to the old double-lip seal.

Any suggestions?