Nice merc! Now that is what i call a roomy stw.
I would get the injectors and fuel pump/fuel pumps timing checked and maybe adjusted. It might bring some power back even.
You mentioned on the "introductions" thread you are getting 23mpg, sounds way too much even for an automatic.
Also, check for possible brake drag.
I once had a 124 myself, sedan with 2litre diesel+4speed manual. Sluggish but reliable, one of the best cars i had
