I specilize in the electrical/computer systems in any brand of auto except VW (I refuse to work on a VW, lost all the money I can afford on them). But I also do most anything the customer wants including mechanical. In the last 19 years I have cultured many good customers who come to me when they have a problem of any kind. This takes most of my time. I spend the rest of my time working on electrical problems.
I have several customers that own MBs and I also repair/maintain them. When I bought my 84 500SEL I only paid $500.00 for it. Half of the engine was under the hood, the other half was either in the trunk or missing. I pieced this car back to life with whatever used parts I could find. Of course, any maintaince type parts (brakes, hoses, etc) were new. I will have to say after about a year, this is the finest car I have ever owned. Also, I have learned more from this car than any other I have ever worked on.
I have seen many leaking injectors on many other brands of cars. Some only affect idle, some cause other running problems. However vacumn leaks are the most common idle problems. But usually, they idle bad any time they are idling. I believe I remember that yours idles good at first, then gets bad after a short time. Is that correct? I'm sure there are other things that can cause this but injectors (or float level on carburators) is the only one I have ever seen.
Checking the plugs is the best way to find this problem. When you get time to check them, let me know what you see and we will go from there.
84 500 SEL (307,xxx miles)