It appears you have a superceded version which drives the belt pulley from the rubber balancer. That would help explain the rubber failure. This is similar in concept to the 112/113 engines where the pulley is bonded to rubber which is bonded to a flange which is connected to the crankshaft. Since the earlier versions failed with regularity it is considered a "wear or service item" by MB. Your problem is that the cost of the harmonic balancer is astronomical whereas the list price on the 112/113 balancer (part superceded due to problems 6 times by my count) is currently $84. My guess is in 15 years we will be paying $900 for the 112/113 balancer. Yikes! Mark