Whats the Service History? Is the oil clean?
There is a problem as stated above with the tubes!
One Quick fix if its lifters... is change the oil except leave it one quart low then refill the last quart with trans fluid as We did ths on SEVERAL 119s with lifter noise and it worked! AHHH MERCEDES WARRANTY Got to love it!!
It was a Hush Hush in house MERCEDES repair!!
I Would try this for 1000 miles then drain/refill as normal
The chain and tensioner should be good til 110/120 miles
Then do the Rails/chain/Tensioner..