It’s a tight one no doubt but it’s also threaded into the aluminum timing cover so not extremely tight like the front crank bolt. You’ll probably want to use some carefully directed flame to get the bolt heated up then break it loose. I find the ole “blue wrench” very handy a lot of times. Plus, isn’t one of the formulations of thread locker meant to be heated to release?

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Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"