If it's running bypass oil to the cooler -8 is probably ok.

If it's the main feed from the pump to the engine you're lucky it hasn't spun all the rods out of it.

My builder does a pile of go fast marine engines with remote filters and he won't run less than -16 on those. He had a customer come to him with a pair of 540 BBC from another builder. 1 blew up and the other mortally wounded. This was after blowing up a fresh pair before. Cranks burnt right out of them. -12 hydraulic hose to and from the remote filters. -12 hydraulic is a good bit less than 3/4".

New engines plumbed with -16 Russell and no more blue crankshafts. At $30K a pop, that was lesson hard learned.

Kevin