I Would Say INSPECT The CRANK PULLEY! THROWING/Chewing up The MONO BELT!
MB Is HAVING PROBLEMS with the V6/V8 Pullies (THEY ARE THE SAME) The Ring around the Crank pully will show wear/cracks and Will Come LOOSE as the Crank pulley is a Two Piece Pulley!! And When It Does WATCH OUT! The Pulley Will TAKE OUT the Front cover/water pump oil pan and anything else in its way out!