Just replaced my tranny @ 330K. Had a used one installed that came from a salvage yard I have used in the past. The guy I dealt with had actually driven the car a few days prior to dismantling, and said he was very confident in it. After installation, it starts off in first just fine, but slips while shifting into subsequent gears. It appears to be just fine if manually moving forward through the gears. This seems very similar to vacuum issues I have had in the past. I hate to have this tranny pulled and replaced if there is a possibility that vacuum is the culprit.

 

Update - Salvage yard sent me a can of BG transmission additive gratis. Said I will need to drive it a day or two to see improvement. Takes off in first just fine, but when it moves to 2nd and 3rd, there is a hesitation before it engages. Could this possibly be the modulator. If so, how difficult is it to change. I still have the one off the old tranny.

 

As previously stated check your Vacuum First next before you start trying to fix your trans mission by replacing parts make sure it is adjusted the best you can.
Remember it is a used Transmission; adjustments and replacing Modulator will not fix internal Issues.
If you have not done so changing the Filter and fluid is another place to start.
Here are some articles:

Automatic Transmission Adjustment Article
http://www.continentalimports.com/ser_ic20242.html

http://www.mercedesdismantlers.com/7...justments.html

If you do decide to replace the Modulator also buy the Plastic Modulator Pin. I has been said the Old one most often breaks when you try to remove it. If you have time to let your car sit waiting for the new pin you can buy it after it is broken.

There are Spring kits made by Superior that has helped some but again check your adjustments firs.

 

That was the clue I needed. Actually, the plate on top of the accelerator linkage that connects to the transmission had popped back over the tab that controls it, thus rending it useless. The tranny was in essence disconnected from the throttle. Just a matter of tweaking the linkage and modulator.