First make sure you are not leaking at the rear of the valve cover.

The rear sealing is much different from the front seals. There are two o-rings behind the distributor. One is small at the end of the shaft that I think is actually a vibration dampener and a large one at the base of the distributor that can and will leak. In addition, there is a miniature seal inside the distributor in case you find oil in the cap. I would not worry about a small amount of oil in the cap.

Replacement of the two o-rings is very easy. Remove the distributor, note the offset pin orientation at the end of the distributor shaft and replace the o-rings. I bought a 940, which was maintained by a good shop, and I found the large o-ring had a good smear of RTV. I found it easier to remove the distributor, easier to install plus the main reason, to help prevent leaks.

Instructions on replacing the small distributor seal are in the FAQ. You should have a special fixture but I did manage to pound out two pins on a piece of hardwood before I had a fixture made.