Oil in the oil filter housing?

[Russell]

Hey guys, just going over the 74 I bought here. As I expected, the cab is in sorry shape underneith, rocker panels have been replaced with slip ons, floor has some tin to replace where it was rotted out, cab supports are basically gone, etc etc etc No big worry as my 80's cab will be going on instead. But yeah, I popped off the air cleaner lid to take a look, and while the filter is real nice, the air cleaner has a ring of black motor oil inside of it... I remember reading about this sometime before, but I can't remember what causes it.

The truck sure starts and runs nice though, its got my 80 beat for sure there...