The rubber bond in the harmonic balancer can decay, which causes the balancer to move and work its way toward the timing cover. If the balancer comes into contact with the timing cover while the engine is running, it will fracture and damage the cover and potentially other surrounding parts. The harmonic balancer should be inspected at every service.Google+
Car Problem Reports
Mercedes-Benz C43 AMG Harmonic Balancer May Fail and Damage Timing Cover
Mercedes-Benz C43 AMG Problem
Visitor, 1999 Mercedes-Benz C43 AMG, 40,000 mi
Rubber ring coming off of harmonic balancer at 40,000 miles.
Replaced under dealer recall.
Rubber ring came off again at 50,000 miles.
Replaced by independent shop using Cortex brand balancer $350. No problem so far.