LOL. "front timing cover" as if there were a rear one.

I have used Aviation sealant on nearly everything over the years with good success. The last few years I have used a (Permatex?) product called "Great Stuff" maybe? It is super strong RTV product that has not leaked for me yet. I have used it on a variety of things on our race cars and sometimes have difficulty getting it back apart. This is a good problem to have.

Best of luck and I hope you have a sense of humour.

__________________
85 300D 3 pedal. Current project.
83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.