Can't seem to get a M103 rear main seal to last more than 4-5 years. Bummer.
I really think the leak occurs around the seal cover/block interface, not the seal ring.
I have always used Permatex black. Maybe not the best thing?
I also use Permatex black on the front timing cover, and it also lasts about 5 years.

Did a thorough search on the sealants, but still confused.
The cover is metal-to-metal, so may need an aneorobic sealant?
But the base of the cover rests on the pan gasket, so needs a conventional gasket sealant to mate there?

The M103 book says 001 989 45 20 10, but that's probably been discontinued for 20 years.

Gurus here recommend Loctite 5900, which I think is aneorobic - but I have had zero luck finding it, except maybe by the case for $300.

Others say the new Hylomar formulations are good, or the current MB 003 989 98 20 10; but I can't find out much about it (except it's $$$$).

Any thoughts?? - don't want to do this again for awhile.

Tks,
DG

If you have been using an rtv based sealer that is your problem. It should be an anaerobic type. Also hopefully you have not been using anything aggressive to clean the aluminum "housing". I use loctite brand "case sealer" on all my stuff. I have a tube on my bench at work, can't think of the number for the life of me at present. I will look tomorrow and forward it to you. Also clean is the thing, I wipe everything down with laquer thinner prior to assy.

ps--if the mating surfaces are out of whack, you can dress them up on a piece of 400 wet/dry (wet) on a piece of glass...

What is an example of a common anaerobic type?

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Jim

you may want to try the black sealant from mercedes benz. It comes in a white plastic tube and comes with funnel type tip and black plastic tube pusher tool.

DG, I second the MB black sealant. Used it when doing the upper timing chain cover on a 104 engine and had no more oil leakage. Be sure to get the mating surfaces super clean,true and dry before application.

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Fred Hoelzle

Just make sure the M-B sealant is fresh. It has a shelf life of one year and will get very hard to squeeze out of the tube after that. The tube is dated.