The rods on the tensioner strip out and is very common. To replace the rod the complete tenisioner assembly has to come out. The means power steering pump and brackets. I have always had to remove the radiatior to work on the front engine on my 190 2.6. Thats if you don't want to damage the radiator (very expensive). The radiator removal takes more than half the time of the other repair. I have done the water pump, scary but when done quite a sense of accomplishment. I did not replace my tensioner but replaced the rod when I did my water pump. My tensioner started acting up a few months later but I can live with it for now.
My tensioner rod was stripped but I rigged it to tighten by placing a spacer where the adjuster is to catch some good threads on the rod. I used a 1/4 inch U bolt that is used for cables on garage doors. I used a Dremel with a grinding bit to make it fit. It worked and would have contined to work. Hope this helps.
1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T