[cleszkie]

I had a high performance 383 SBC built for my Blazer - full roller, one piece real main, oil dipstick hole on passenger side of block. The engine came complete from intake to oil pan, EXCEPT they didn't provide an oil dipstick. So I went to my local parts house and grabbed a dipstick that had the year range that my block fell under. Long story short - my engine leaked out the rear main seal right off the bat! Come to find that I was overfilling the crankcase with oil based on markings on the dipstick that were not correct for my block. My static oil level was up over the rear main seal! Did some more research and found another SBC oil dipstick with same year range of application with the oil level much lower on the dipstick. I verified that this oil level kept the oil below the rear main seal, but the pan full. No more leaks.

Moral of the story - make sure your dipstick is correct for your block. There are apparently a couple variations out there with different oil levels. Rear main seals are not intended to have standing oil behind them.