The transmission in my 1987 300TDT diesel wagon (W124) has always shifted a bit harshly, especially going from second to third gear, and from park to drive. After I installed new Monark injector nozzles, Beru glow plugs and cleaned out the oily gunk from the intake manifold, the transmission now shifts smoothly. It's like I installed a new transmission, but I didn't.
So which of these procedures (inadvertently) solved my clunky transmission? I'm sure it wasn't new glow plugs!