I'm in the midst of a major intake refresh here:
http://forums.pelicanparts.com/porsche-928-technical-forum/707339-good-writeup-s3-intake-refresh.html
One of the WYAIT jobs is the cam covers/seals. I started on these over the weekend and was pretty mystified by the ones on the rear of the motor. There wasn't enough room for any of my sockets, and the plastic 'collars' around the 10mm bolt heads made it almost impossible to get a wrench on them.
After studying the situation a minute, I grabbed a long drift and a mallet, and just knocked the plastic collars off the covers. Old and brittle as they were, they knocked right off with little effort, then I was easily able to get a wrench in there and remove the covers.
With a set of picks and a mirror, I was able to clean out the 574 residue in the cam towers and shine everything up with some Scotch Brite. After hosing everything out with some cleaner and compressed air, I installed the new S4 covers with some Curil T.
If I ever have to do this job again in another 26 years, removing the S4 covers with the engine in-place will be interesting. It is too tight back there too drive a sheetmetal screw into them, but they might come out with a carefully applied pick. Hopefully I won't have to find out.