same thing happened to me. Not all machine shops have a narrow enough stone to grind the the crank while leaving the slinger in place. My motor leaks from the rear main seal area also and there is not much you can do. Good 312 cranks are becoming harder and harder to find. Reduce crank case pressure as much as possible with good breathers and this may help some.

  Ron Lane,  Meridian, ID

I have a 312 crankshaft machined to 292 mains and unfortunately the rear oil slinger was machined off. I have yet to get this thing to seal, and am tired of taking it apart. Any suggestions or should I just try to find another crank?

Jan  Urbanczyk  Major USMC Ret.

                                                                 Bowie Maryland