I own a 1991 300SL. I'm the 3rd owner. Here's what I know. The door locks don't auto engage when the car starts moving like many modern cars do. This may have changed in later years.

It takes a really hard impact or shake to make my roll bar pop. It's only happened once when I hit a curb avoiding a collision: scared the heck out of me. If yours comes up easily, it's out of adjustment. I don't believe the door locks should open on a hard stop. This is no doubt related to your other vacuun problems.

Those flaps behind the doors are adjustable. There are screws inside that allow for some minor positioning. But it is also possible that the top deployment mechanism is out of adjustment. I broke one of those flaps when my top folded the wrong way due to a screw head breaking off. The hinges and pivots of the mechanism need to be well lubricated with white grease or similar. If it binds, you'll have all kinds of problems.

If the vacuum hose has a "block", just reconnect to the lock. The actuators in the doors are the most frequent failures and can be the source of a leak. In the truck is a manifold / router from which vacuum is distibuted. With a vacuum guage, check to see if the system holds vacuum. If you have a hand pump vacuum guage, you can check each hose leaving the manifold to track down a leak. You can also use the pump to excercise any suspect bad actuator or vacuum motor; a good tool to own and not expensive.

__________________
Resistance is Futile.