I used silicone used on valve covers. It does the job fine. It's not a problem if you want to remove it later as easily peels away from the gasket once you have it off.

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1992 Mercedes 190D 2.5 turbo 5sp manual. EGT+boost gauges. Boost controller set to ~14.5 psi. 1 1/4 turns on full load adjustment. LPG injection. Next in the list is water injection.