When removing and reinstalling injectors, use new "heat shields"...these are actually little compressible washers that the injector seals against. Its a good idea to get a bunch of these to have on hand...buy from mail order (Mercedesshop) for cheap...dealer wants a lot for these (as with most things). Also, before installing, make sure that the injector hole is very clean....a little piece of sand will prevent good seal and will impair operation. Dont, put the little disks in backward....when removing injector see position of the ones in the car (convex side toward engine, flat side with compressible rim toward injector) The injectors need to be torqued properly (I forgot the torque setting...look in Haynes or other manual)

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)