Rad-Man,
I still recommend NGK, but you shouldn't be having any problem with any brand.Mark's thermostat is a good one,andyour engine takes a 79 deg thermostat. You also have a thermostat on top of the inj pump. When the engine is cold it allows extra fuel and air.Unscrew the little filter thingie off the back side of the pump,I think it takes a thin 22mm.It has been so long since I've worked on any M130 engines that I can't remember.With the engine at full operating temp put your finger over the threaded hole.There should be no change in the engine.If your finger gets sucked in and the engine dies this special thermostat needs to be replaced.Notice I said SPECIAL,and we all know what SPECIAL MB parts cost.Also put the little filter thingie to your mouth and blow through it.If your cheeks puff like a tuba player,it's plugged and the car will run extremely rich.Also the cold start valve on the intake manifold could be dripping.Bottom line;Mark is right on.Find a good shop in your area that knows vintage MB's.If you go to a shop that is loaded with scanners and techs under 30,you're in trouble.You need a facility that has an old fa*t like me hanging around.
Good luck,
Peter

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