Rick-

Just curious, at what mileage did this occur? I feel your pain. My 450SLC broke the driver's side upper rail. I was a little luckier, limped in to mechanic before bending valves (jumped only one tooth?).

I wonder if a stretched/loose chain slaps around more especially when there is less oil pressure at the tensioner, and a chain slapping a brittle plastic guide exacerbates the problem.

Dang this design! What's the point of using a chain as opposed to a belt if it has these weak plastic guides?

Best of luck.