oil....air filter...why?

Hi, so i am looking at buying a 95 golf 2dr 2L 5spd. The price is right at $1600 and so far, everything seems to check out ok, but there is a little but of oil in the air filter. There is only a very small amount, but it was enough to be noticed, and no oil in the air filter is good oil. But what i want to know is what causes there to be oil in the air filter and is it an expensive fix. If it doesnt cost to much for the part(s), i would really like to purchase the car. Thanks for all your help.

Jon

I can probably be caused to the breather hose that comes from the valve cover what makes oil coming into the airbox. Is not and expensive repair and 1600 for a 2.0L ABA Block!! Man, i hate you.

Anyways, make a compression check for low compression as well as a oil pressure test, and if it does good. Go for it, is a steal.