mrkozzy,

If this were a 123 car I'd be ready for you. You should be able to find a vacuum line schematic. With the schematic in hand and a vacuum tester from the Auto Parts store, you should be able to trace your problem. If it's anything like a 123, start where the supply line goes through the firewall. If the whole door lock system won't hold a vacuum, go halfway, which is probably the line leading to the right doors and try there. If it holds a vacuum there, go back toward the source, if it doesn't go to the back door. Continue splitting the system you've tested in half until you've homed in on it.

Good luck,

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Larry Bible
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles