I don't know if you've fixed your problem yet. It souds as if you installed your distributor incorrectly. IF you take a piece of chalk and make a mark at the TDC mark in the crank and roate the engine by hand until it lines up with the timing pointer behind the crank you should be at TDC. Take the distributor cap off and make sure that the rotor is pointing to the #1 plug wie. The is also on mine which is a 77 450sl a notch on the distributor to line the rotor up with. As far as the vaccum door locks are concerned they are notorious for acting strange. I took my door panel off and lubed the linkages with white grease and they work beautifully now.

jmdunn