My later type oil pump cover sent me on a freakin' wild goose chase when it developed a hairline crack in the top left counter-bored hole.
It presented symptoms of a leaking rms or worn guide ring or guide ring o-ring.
I was advised (by GSPD) to run the motor without the tranny and clutch installed. Bingo! the leak identified itself almost immediately.
The earlier angled counter-sunk type covers could not present this issue imo.
I am proud to be the recipient of never before heard of airhead problems. True pioneering