Glad you asked the question.. mine is doing the same thing. I get oil around the cap but not enough to affect the level on the dipstick. I was wondering what was causing it and the only factor I deduced was the cap.. but was afraid it might be some bigger problem. hope changing to a new cap will solve the problem.. I haven't replaced mine yet, but will soon. Thanks guys.
1982 300D (266,001 mi.) looking and running great
1976 450 SLC
1982 Jaguar XJ6 (loved, but gone)