This transmission slips from 2-3 and 3-4.
I'm going to change the transmission filter and fluid. Is there anything else I should consider doing while I have the pan off.

I'm also going to replace the vacuum modulator with the updated version. That might have to be done on a different day.

What else should I do while under there??

Consider adding Trans X to clean the valve body. Drain the converter too.

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It may be a vacuum issue. I had a decent 1-2 and moderate 2-3 flare. Replaced the vacuum gizmos and the transmission is now flawless

Tell me which vacuum gizmos you replaced.

Also, isn't there some kind of B2 piston that affects it?

I just did two

There’s one on top of the cam cover (valve cover). It’s under a black plastic box. There’s another on top of the IP which is NLA. IF you can find one brace yourself for sticker shock

My thread has pictures on China Blue

As greazzer said, don't rule out vacuum. Too much vacuum will make it slip quite a bit, and just all-around sloppy.
An easy test would be to disconnect vacuum entirely, it will will shift quite hard, but if the slip is removed you now have a clue.

Sun Valley Mercedes Transmissions has an excellent website with tips on common issues with Mercedes automatic transmissions. mercedesdismantlers.com

The owner is Marc and he is very helpful.

OK< so, I disconnected the vacuum. That cured the flare from 2-3. But, the 3-4 flare remains. Also, the down shifts are rather hard now. So, now, my concerns are the 3-4 flare and the rough downshifts. I wonder if new fluid/filter will help.

I suggest you track along the advice given here and also look at the information from Sun Valley. The initial level set is fluid and filter change which includes the torque converter drained. The latter should be done anyway at the intervals in your owners manual. There are a half dozen points where you could have a vacuum loss. I would get a gauge and measure your vacuum from the pump back to your modulator. Pray you do not have the red capped one since they are NLA and their occasional appearance on e B a y makes you not appreciate Mercedes

Thanks Greazzer! I hope to get the time to get under there soon. I'll look at the modulator too. I have the redesigned one ready to install. But, in this coupe, it is a bear to get access to. I might need to lower the transmission to get to it. This photo of the modulator makes it looks way easier than it is.

Thank goodness you don’t have the red topped one. I would do the fluid and filter first and try to isolate things versus doing a bunch of repairs all at once. I would hit one of the chain auto parts stores and get a half dozen cans of brake cleaner too. Buy a meter of the correct metric vacuum line and after you do the fluid and filter change work your way from the vacuum pump to the modulator. I had a pretty noticeable flare 1-2 and moderate 2-3. I followed the above and now it’s perfect and shifts without even feeling it

Is there a source for diagrams for the vac lines for various models? Lucky I am that so far I haven't had any issue, but I'd like to bank those diagrams for hen the day comes

What is the correct line?