the tan paste is common, moisture usually condenses there, the valve covers have two pieces that usually leak , neither are hard to do, just can be time consuming, hoses can break if brittle etc... the upper part of the valve cover is seales with mercedes black silicone, the few i have resealed i recall the upper part of the valve cover can be difficult to remove, the silicone usually hods it on pretty good, if possible try to use original parts.

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1967 250 S
1967 280SE
1968 250S
1971 280 SE
1973 220
1974 280 S
1975 450 SEL
1976 220 D
1979 300SD
1983 300 SD
1985 230 TE euro
1986 280SL
1986 500 SEL euro
1986 190E 2.3
1990 300 SE
2003 C230 K
2004 C230 K
1987 560SEL
1987 300SDL now in canada
2005 C230
1998 C43 AMG Sold to DON
1993 190E 2.6
300TD Former daily driver Totaled
current:
R320 CDI
Ram 2500 Cummins