Looking up an image of your tensioner, it looks like it should come apart for cleaning. I redid the tensioner in my OM603 for the same reasons as you. Varnish was the enemy, everything was clogged up with it. Since cleaning, it's been fine.

WARNING: Make extra special attention to the FSM on the installation procedure for your specific engine! Some tensioners have a specific installation method and can ruin the chain or camshaft if installed incorrectly!

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)