I was toying with the idea of changing the camchain tensioner, guides and rails on my 85 380 SE as it had 156,000 km and the parts were original. From what I have read here and elsewhere, 100,000 miles (160k) seemed to be a good time to do it for preventative maintenace. Given the Canadian Winter and a lack of heated space, I decided to let my local non-dealer MB tech do it (and replace the timing chain at the same time if the stretch warranted it).
I was shocked when we pulled the valve cover and one of the rails came out in chunks. Wow. I guess I was extremely lucky to catch it in time before it got caught in the chain and wrecked the head.
My suggestion to anyone with such a car is if in doubt, get to them ASAP.
BTW, Euromotion here in Toronto is a great choice for the work.
Good driving to all.
John