Sounds like a air leak most likely. If it was a crank seal it would be on the left side considering that is the dry side where the stator is and air would come in that side. If the right side crank seal was bad you would have a rich condition on your right side from the oil coming in from the clutch side. I would try doing a leak down test. Plug off your intake and exhaust with a rubber cork or anything that makes an airtight seal. Get you a hand pump vacuum tester, put piston at bottom dead center and pump it up to no more than 9 psi and you should have no more than 1 psi per minute leakage. Use som soapy water to help find the leak. Check your cylinder base and head gasket,where top and bottom cases come together,reed gasket,and around where you sealed off intake and exhaust.