Your vacum door fix is fairly easy to do. The pump is under the rear seat. I dont know the price of the pump but it shouldnt take more than an hour to swap out the pump. I recommend you call around to some MB mechanics and state your problems. Don't take everything to get done at once. Build up trust w/ the mechanic. Start w/ the door assist. But before you do that try this fix I got from bekkers catalog. With key removed, remove fuse 9 from the trunk fuse box and re-insert. This resets the system. If this doesnt work most likely it is your pump which has grown tired from pulling your armored doors in all these years. By any chance what do you need an armored car for anyway?
I dont know if it is related to my post but here is a reason to always try to watch your car being repaired. I was at my mechanic and I was looking at another technicians pulling the dash out of a 420sel. He took it out in less than 5 minutes. He then commented to his partner that they charge 5 hours for a dash removal. A while back at the same joint, I saw this Hemmingway looking guy overseeing the repair on his F355 to change some vaccum pump and the technician worked so dilligently and fast that I was dumbfounded.