From what I've read the 3inch main blocks were machined well but some of the 3.25 inch blocks had trouble in the rear seal grooves. The grooves were either not true/ round or they were not on the same centerline as the crank. The rope seals would fill the discrepancy but the more rigid lip style seals cannot fill the void and even a correctly installed one may leak. Mine did.
I read about that as well.
However, tonight I changed out the hard rubber plug in my left valve cover for the standard breather I had ordered with the valve covers. I fired the car up and idled it for a good 10 minutes in the garage (did not exceed 2000 RPM). No Leaks.
Looks like I have excessive crankcase pressure which, according to the PY archives, is not unusual for a newly rebuilt high HP Pontiac motors.
Next will be another test run with speeds above 40. If this breather changeout does not work, I will need to get another breather with a nipple and run a 2nd hose to the air cleaner. That should vent the crankcase enough to keep me from forcing oil past my rear main seal.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
