Thanks for sharing that with us, Jim. When I did my water pump and cooling system, I took things apart and found RTV at a lot of the seals. I cleaned off the RTV and dressed the mating surfaces, scraping everything off, finishing with scotchbrite. I then put a thin coat of silicone on the o-rings, nothing else. Just enough to make them shine. I don't like installing seals dry. I learned as a kid reading Machine Design that some pressurized joints require o-rings to slide into a certain position within the groove for proper sealing (not that cooling systems are highly pressurized). I figure the silicone would allow the o-ring to relax into it's natural position.

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95 E320 Cabriolet, 159K