My neighbor's starter on her 300TD would barely turn so I jumped into the problem with my usual reckless abandon. When I looked down at the starter from the top I could see that the top bolt was unbolted and the bottom bolt wasn't as tight as it could be. Thinking I had solved the problem I attempted to tighten both bolts with only a modicum of success. In the meantime I charged up the battery with my charger while working on the bolts. I should mention that we tried to jump the car with cables as well resulting in the engine barely turning for a one second and then resuming the clicking noise from the what I would presume is the starter solenoid. Even with a charged up battery we had the same result. My diagnosis is thus: I think she has a dead starter which will do about the same thing no matter how much voltage you put into it from any source. Any thoughts on this?
Thom