This 1995 s500 sedan has about 120,000 mile with the tranny fluid and filter recently changed but has started to show a progressively slow response when shifted into reverse. It takes two to five seconds to start moving into reverse from a level surface( it takes longer to move when it has been driven). Once it starts moving in reverse the car gets its normal power, but if it is on an incline, I am not able to engage the car to move. Forward shifting seems to be fully responsive with no problems. The check engine light is also activated, which I think is caused by the slow reverse shift problem.
Does anyone have any advice on this one?

I would imagine your reverse clutches are shot. Pull the pan and look @ the residue, then follow the metal-type/size chart. It's usually dead on.

I think if you pulled codes, you'd probably see the tranny controller griping about shift "Delta", or clutch engagement speed.

If it's any consolation, I've replaced trannys in 110k mile 140/119's before

Sounds like two different problems - 1) your transmission is going to need to be rebuilt soon, and 2) you need to pull the CE codes on your engine.

Well documented reverse problem for 722.5 transmissions (and maybe other models as well). I recommend having it rebuilt by Silver Star Transmissions in OK. There have been upgrades / service bulletins by MB to fix this problem as well. My experience and reading has been, once your reverse gear starts to slow it's only a matter of time before the trans. must be taken out & rebuilt. Just my 2 cents worth.

The EC taken by the Mercedes dealer suppusedly came up with a faulty neutral switch indicator, and they change the neutral switch at a cost of about $400.00 but to now avail; the check engine light has reappeared! Now they want to retake the EC reading to see "if there are any new codes", but I have my doubts as to the veracity of their mechanic. Another neighborhood mechanic that works on Mercedes did an EC diagnostic a few months ago and told me that there was a problem with the "knock down cable" causing the check engine light and possibly causing the delayed reverse shift problem. Does this second opinion sound like it may be the answer to my problem?

Anyone charging $400 for a neutral safety switch should not be trusted to read your fault codes. You should build a code reader and read them yourself.