Audi 90 2.0 5-cyl Oil In Air Filter!

[ian2000t]

Just doing a quick service on my Audi 90 2.0CD 5-cyl with Fuel Injection. I only bought this car a few months ago as a cheap runabout but when I took the Air Filter out to change it the old one had oil in it! Is there a reason oil is being blown into the Air Filter and should I be worried?! It has done about 160,000 miles. I've heard that it would pressurise the oil and force it out through the Air Filter if it holed a piston, but I assume I would have notced this? I was also told that it could be worn piston rings. Is this a big problem or will she keep on going? She runs well apart from a slight stutter when you put your foot down at low revs.

Thanks for any help,

Ian Thomason