Yes, lack of door locks indicates a vac problem (or just busted door lock diaphrams).
You really need to spring the $35 or so and get a MitiVac at the first opportunity, makes life very much easier (so you can find out what's wrong with the tranny, for instance, rather than replacing blind!).
You must pull the driveshaft to replace the center bearing and support, and pull it apart. MAKE SURE YOU MARK THE FRONT AND REAR HALVES!!!! if you get it even one spline of, it may shake like crazy. Use a paint pen and PLEASE make sure the marks don't wipe off (this is the result of driving my 220D with an unbalanced shaft from screwing this up, sorry about the caps!).
To remove, mark the flex disk and driveshaft tripod, the remove the three bolts front and rear. Leave the flex disk in place. Loosen the slide clamp with a very large pair of channel-locks or a pair of pipe wrenches and then remove the bolts or nuts that hold the center bearing carrier in. You may also have to drop the exhaust and unhook the parking brake cables. Compress the front half of the driveshaft toward the center bearing until it comes off the pilot on the tranny flange, lower the front, and them pull off the rear pilot.
To replace the bearing and carrier, you must pull the shaft apart, the remove the snap ring retainer and press the bearing and carrier off the back part. Press new one one, install carrier, replace snap rings and boot, then re-install the front half. Splines mush go in original locatoin, and unlike Volvo, MB doesn't key the shaft!
Installation is the revers of above, with the exception that yyou must roll the car back and forth on it's wheels before tightening the clamp nut -- if the shaft isn't preloaded correctly, it can shake.
Old benzes aren't really bargains once you start getting them back to factory condition.....
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!