Your car was equipped with a transistor box under the fender. It is part of your ignition system. Maybe that is the problem?
Mine went bad many years ago and the cost to replace it is rediculous even by third party outfits. Two options around this that I know about
1. convert over your system to standard breaker point ignition. This is the lowest cost approach as you will be bypassing the defective transistor box and ballast resistors. You will have to replace your coil with another model coil (if you need the Bosch model number I can look it up) and you will have to use a condensor like the one that originaly came with your car's distributor but was later eliminated by MB mechanics. The condensor can be special ordered at Pep boys for your car for about 3 dollars instead of about $60 at MB. Don't worry about the performance of the condensor from Pep Boys it works fine. The job of the transistor box is to add longevity to youir points by minimizing the point damage (arcing?) during car starting. Points are so cheap and don't need replacing that often anyway (I do it every 12K) that I consider it a very small price to pay. My 1972 350/450SL runs fine at all speeds with this "fix".
2. The other solution which I would do if money didn't matter is to change over to an electronic ignition system. Check out this website: http://www.durranceeng.com/
He really seems to know his stuff and the site is packed with info and he can sell you what you need.
Regarding the trigger points at the base of the distributoir:
They have nothing to do with the ignition system. They control the fuel injection. Take them out and clean the points with an ignition file. Since they operate at low voltage (unlike ign points) they last a real long time. They are very expensive to replace (unlike ign points). I don't recall but there are either 2 or 4 points. Some of the points you can get to but one or two are covered in a small plastic box. To get to that point you need to cut a slot into the transparent plastic box to allow you to slip in a small ignition file. I don't recal if I used a mini solder tip or my dremell to make the slot.