I own an 83 Turbodiesel for 8 months now with 89,000 miles and I really enjoy driving it. I really like the w123 body. The car sometimes makes a banging noise that seems to come from the rear when I brake to slow down and it downshifts from 4-3 gear. I also started getting minor vibrations above 40 mph. The vibrations are present even when the car rolls in Neutral at that speed. I had the transmission rebuild not in an MB shop and the banging(clanking sound) problem and vibrations still exists but not as much. Could this be a vacum issue adjustment and not the trans or maybe a transaxle/shaft problem? I took the car to a local MB dealer and recommended rebuild trans by them($2,000) or replace it with a refurbished one from the factory($3,000). Any recommendations are greatly appreciated. I really do not want to sell the car since it has no rust and no other problems. Thank you in advance.