Are you talking about rear seal leaks?? If so, just the nature of the beast. All mfrs had issues with early rear seal drips. We're cranking more horsepower out of FEs now (strokers & radical roller/flat tappet cams) than ol' Shel ever invisioned back in the day.. That leads to increased blow-by, among other things. With an inadequately designed rear sealing system that just means more
oil out the back.
Your question was somewhat vague, hope this addressed it.
Dave