The rubber portion of the harmonic balancer pulley is known to fail on the earlier M112 and M113 engines.
Do a search, there is a ton of info.
You can install the new one for about $400...
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".