I had a really nice 115 240d which had so much wear in the spline that attaches the injection pump to the sprocket on the cam chain.
that it allowed the timing to slip a spline....then it would slip again. The splines would hold a while so the car would lot drive fine but put it on the highway and soon it would lose power then barely run at all. It is a sort of coupler with female splines on both sides, input and output.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.