Yeah, I'd really of course rather stay off the road until it's fixed. I drove out to the jungle, then I had to drive back. No mechanics or even auto parts stores out there. Hmmm, what is this check valve part number? Or a link on an auto parts store?

EDIT: Does my 1985 model have this check valve? None of the parts websites show it for my model.

Thanks,
David

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1985 300D. 179,000 miles.

I would replace the master cylinder.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

A problem with the check valve would affect the vacuum boost. That does not appear to be your problem.