318 LA rebuild after losing a valve seat

Well, I’m not sure why the rear main was leaking, but I replaced it. It wasn’t a huge leak, just the tiniest bit of oil that would form maybe two drops a day. I don’t understand, because shouldn’t the oil level be below the seal?

If I added too much oil and the level rose above the seal, would that cause a leak in an otherwise good seal? I think I goofed and added 6 quarts, because when I did a google search of “318 LA oil capacity”, the first result is 6 quarts. But I think that’s for the trucks that have the 318 LA.