2009 MB Diesel just stalled and won’t start

[Citroënbender]

I’d assumed they had done a partial teardown which included the cam covers. That would reveal the failed rocker arms. Honestly, something would need to be seriously wrong for damage to extend beyond that. Because the valves are perpendicular to the piston tops and of stout design, is why stuff breaks in this way.

After throwing out so many water pumps, cam belt idlers and tensioners that were probably perfectly good (belts changed by age, but low mileage) these days I often think a bare belt is sufficient - if the other parts have not been pressure washed, solvent cleaned or allowed to corrode. An informed examination is key.