Common Oil Leak Sources

Didn't find anything on this with a search. Saw a couple things about replacing the oil pan gasket. Also remember reading about the low oil level sensor possibly being a leak source.
The wife's 525 is leaking oil and a general inspection doesn't seem to pinpoint a source. What are the usual sources? How have you located the source? I've not used the UV dye thing and I (surprise)don't have a black light on hand...

The valve cover gaskets are a good candidate.

Does anyone else have bad (and worsening) oil leaks? Seems like the front and rear crank seals are leaking and it's getting pretty bad. Anyone solve the problem?

Mine was a head gasket...

Scott

The oil filter housing is a likely suspect. I did a search and found some good tips on how to DIY. I figured I would do this while I had my cylinder head out.