I put a rebuilt transmission in my '80 300SD and the rebuilt was as different as day and night and all for the better. The rebuilder said he used all the latest level rebuild parts. It works great.
Cost was about $1200 including new vacuum valve and rebuilt torque converter. I bought it direct from the rebuilder and put it in myself. MB wanted about $3000 plus tax for trans alone. They know where they can stick that. Maybe that's why they wanted to close this web site.
P E H