I just ran into this repair manual for the E23, where a "vent bore" for the oil pump is mentioned.
This is supposed to reduce the time to build up pressure.
Interesting, I'd not seen or heard of it before although it does appear in my E12 manual. I "guess" it can be airlocked to a degree and the bleed hole diminishes or eliminates that. I have had problems with the light slow to go off, but I attributed it to 300K oil pumps.
Sometime ago a friend had a verrrry slow to go out light and he replaced the oil pump. He did find bits of the timing chain guide in the pan and maybe the pickup, but said with the new pump it went out right now. He was certain the pump was the problem.
air and trying to shove that out through an oil filter I can see causing trouble. If the pump internal clearances are excessive from wear though, the real problem is the pump. Doesn't take a whole bunch of extra clearance in there for it to stop pumping correctly. I've had to replace fork lift hydraulic pumps a few times from that, the wear in those is enough to feel with your fingernail but its probably only a couple thousandths of an inch at best.