I just want to share my experience with my 1995 525it, M50: I had 2 plugs with old brittle o-rings leaking oil- lots of oil. I bought new o-rings at the dealer and tried to change these o-rings at the plug which is secured with snap rings. I had to remove the oil filter housing in order to get to the plugs which is causing a pain in the neck.
I failed. Oil was leaking out again.
The I opend it up again and run a calculation by Trelleborg (the o-ring manufacturer)and found that the o-ring BMW sold me was not big enough to hold the pressure. I think they sold me a 22x 2.5 and Trelleborg said 22x 3.0.
So I installed 22x 3.0 o-rings and did a pressure test with compressed air before again reinstalling the oil filter housing and all is fine since then.
If someone has this problem please contact me.
I also have another perfect oil filter housing with screwed plugs for the M50 if someone needs it.