Yep I can understand the frustration. I have been in the maintenance field since the early eighties and I am still learning. This is the first time I owned a Mercedes though.
The weapon of choice is going to be a snap-on camera that I can get into tight places and have a look see if I have any problems lining it up.
There designs I admire and some I don't. The power steering pump bracket is one I don't love too well.
The chain started slapping when I would go under moderate load but no chain guides broke.
The chain tensioner is known to wear out and the new one I have has needed tension. Tho old tensioner will not resist fully rearward in travel like the new one. The old one is getting laid to rest.
I am sure that #1 these chain tensioners can be rebuilt. #2 if neglected in the state this tensioner is in then the timing chain will wear out very quickly.
I am going to replace the tensiner first and then the chain guides and then the chain and sprockets. Its hard to pass up on sprockets at 25 bucks a pop.
I will probably make a table lamp out of the old sprockets and chain and use the tensioner as the push button.