oil in air filter

What could be the cause for oil in the air filter of a 93 grand am. Took it in for an oil change and that is what they told me. I haven't noticed it smoking. Does it have a pcv on it? Also, how hard is it to change the thermostat in it? It is a friend of mines car that I am trying to help him with it. Thanks for any help.

sounds like pcv valve to me,also install new air filter,and probably wouldn't hurt to clean throttle body,or your gas petal will stick down the road and create some driveability problems.Good Luck Mike

Wouldn't it make it easier to help you if we knew what engine you had??