I mean because the 210 check valve is part of the fuel pump, if the check valve goes bad, you have to replace the entire fuel pump assembly including an otherwise working fuel pump.

I don’t know if this is practical or safe but you could test the hypothesis with a check valve along the fuel supply hose to the fuel rail. Or clamp the hose immediately after shutting off the engine then release it immediately before starting. Nah, get a fuel system pressure tester.

Sixto
98 E320s sedan and wagon