I just had the harmonic balancer done on my '98 ML320. I took it in for a B service and specifically asked them to look at it. They said it was just beginning to "wobble" and they replaced it.

The new part numbers:

112-035-13-00 Vibration AB
006-990-70-04 Screw
112-997-02-46 Seal Ring, V
023-997-84-47 Seal Ring

They covered the replacement but only after much discussion and complaining, since I already was spending $2300 on service and repairs.