well I took the old belt off and it was a 2415mm belt. so either the MB manual is wrong (or generaically written) or the previous owner, an MB tech for the largest MB dealership in ATL, fell into the same trap as myself. I installed the new 2415 belt and everything went swimmingly. Nice and tight with just the right ammount of deflection. Had I used a 2445 belt, that whole extra inch would make it very sloppy I imagine. than again maybe the tensioner is supossed to take that up. Thats a question for a new thread.