I have taken all the door handles and lock mechanisms off my W126 and soaked them in gasoline to remove the old grease and debris. After cleaning with a brush and re-lubricating them, the doors open and close very nicely. I previously replaced and adjusted all the door strikers, though.

The worst part about having nicely closing doors in your car is that everyone who gets in likes to slam them. I usually give a lecture shortly after...

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge