Chevrolet: oil in the air filter

I have a 78 malibu. I just removed the air filter cover and the insde was
full of oil. What would cause that?

Micheal Artindale wrote: 
Anything in the US after around 67 would likely have a PCV valve,
certainly anything after 71 or so will. If oil it in the air cleaner
it's most likely either a none-functional PCV valve, or more likely
(especially for that age of car) excessive blow by caused by worn
compression rings. Sometimes products like marvel mystery oil can help
with this if it's caused by rings that are gummed up rather than worn,
but otherwise you would need to replace the worn parts. Since PCV
valves are pretty cheap, I would try replacing that first (they should
be replaced every couple of years anyways) then if that doesn't work try
the mystery oil, since it likely that an engine rebuilt would be
required to fix the problem if it's work piston rings. There can be
other causes such as clogged oil return galleries in the heads, but
those problems also usually require an engine rebuilt to correct as
well, although sometimes you can postpone the rebuilt by using internal
engine degunker if it's clogged passages. However, usually if things
are clogged or gummed up that points to poor maintenance which would
tend to have caused engine damage anyways.

Hoping it's just a worn out PCV valve,

--
Cy Welch
89 Camaro RS 5.0 TBI
03 Malibu