Looking at my '87, there appears to be some kind of goop that has squeezed out from between the trap cat replacement and the turbo. [This would have been done at the dealer as part of the trap cat recall campaign.] I don't why you couldn't make a gasket from your sheet metal and use a thin coat of high-temp sealant on both surfaces.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970