I'm working on the cylinder head of my 91 300SE. Allow me to direct you to photos.yahoo.com/tabijan, in the 91 300SE head and valve seals album, in particular the first and third photos.

If you can ignore that I'm using a lousy valve spring compressor, look at how clean the cylinder head is. The pockets beside the valve springs have some deposits but that's it. This car has almost 155K miles on it. AFAICT the head has never been off and it's run on dino oil all its life. Only Castrol GTX 20W-50 since 129K miles. I use my own FSS in that I change the oil when it gets dark, usually 5-6000 miles. A quart and a half of new oil goes in between changes. Maybe that's what oil's supposed to do but it surprised me.

ps1, I can't use the same valve spring compressor to install the springs because the fingers interfere with the seals. In fact removing the springs with this tool removes the seals in the same step.

ps2, I'm replacing the head gasket because coolant consumption exceeds oil consumption and because of external head gasket oil leaks that stink up the cabin through the AC.

Sixto
91 300SE
87 300SDL
83 300SD