Looking up pictures of the 606 tensioner, it's VERY similiar, if not identical to the 603, complete with the aluminum sealing ring. Try tightening the big bolt head (tensioner body) and see if the leak stops. If not, you'll want to replace the crush washer.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

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

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]