I know nothing about your particular model engine....
but yes, even in the shop manual MB expects the most wear to happen in the first part of a chains' life... not to start wearing more per mile later on....
I too am skeptical about measureing to .1 of a degree....

If your tensioner is the same age as the chain I would sure change it...

Does MB supply offset keys for the cam sprocket to correct ( up to ) a certain amount of chain stretch.... as it does for the 616,617 engines ? MUCH easier to do that if all other stuff is ok....