You also need to inspect the part of the Injector that the line seats on. If they are scratched, rusted or split/cracked they are not going to seal.

It is the some on the Fuel Injection Pump end of the lines but with the delivery valve holders.

This is just a wild thought but I have seen complete made in china Injectors for Mercedes on sale. If the Injectors look new perhaps they are the made in china ones.

See if the Nuts on the Fuel Injection hard Lines are bottoming out on the Injector or delivery valve holders.

I believe I haver read that the MW Fuel Injection Pump Hard Lines are different from the M type Fuel Injection Pump hard lines.

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84 300D, 82 Volvo 244Gl Diesel