928Tom

I am replacing the differential cover gasket on my 1978 Porsche 928 automatic. When I removed the cover, I saw bright blue silicon in addition to a worn out gasket. I have the new gasket - should I use RTV as well? Thanks!

GregBBRD

Porsche installed the gaskets dry....on perfect surfaces.
They are paper and will eventually oil soak and weap. Takes about 15 years.
Because the two surfaces are rarely perfect any longer, I use a non hardening sealer on them. (Curil T2.)
Old fashioned Permatex would also work. (Locktite has a version of this.)

Sorry, no experience with silicone sealer.
Not one of my "go to" sealants.

Hey_Allen

Would something like gasgacinch or permatex form-a-gasket (aviation gasket sealer) work?

Those two have generally been useful when I wanted a gasket to stay and seal on less than perfect surfaces..

928Tom

Thank you! How/where would you recommend I lay on the sealer? As in, would I be putting sealer on both the differential surface and the rear cover surface?

GregBBRD

Form a gasket will work fine, here. There's a zillion American waterpump gaskets coated with it.
Gasgacinch is more of a contact cement to adhere a gasket to a surface.

GregBBRD

Put the gasket onto a piece of cardboard. Use a brush to install Permatex, Loctite's form a gasket, or Curil T2. Thin layer.
Turn the gasket over onto the same piece of cardboard and repeat.
Install gasket.
Install cover and tighten nuts to 14-16 foot lbs.

928Tom

Thank you Greg. I’ll do that this weekend.

Daniel5691

Please get plenty of ventilation if using Curil. Whew !!!

GregBBRD

I think that is why the K2 is no longer on the market, plus the warning of not smoking or eating until you had washed your hands.
Great sealant, but most likely "Cancer in a Can"...

T2 is completely different and a bit strange, but I have not noticed a smell.
Tastes better than the K2, also.

928Tom

I installed the differential cover and the battery box today. Everything went smoothly. That advice to use a brush for the permetex was very useful. I would have tried to squeeze a bead around the paper gasket which would have taken forever and been much more difficult. Thank you to everyone for your input.