An exhaust leak may develop due to cracked welds on the front catalytic converter. Replacement of the catalyst is recommended; re-welding of the catalyst is discouraged because it is an emissions device.Google+
Car Problem Reports
Mercedes-Benz ML55 AMG Welds May Crack on Front Catalytic Converter
Mercedes-Benz ML55 AMG Problem
Visitor, 2002 Mercedes-Benz ML55 AMG, 88,000 mi
It is recommended to re-weld the cracks. I can not find anyone in Anchorage that is willing to weld them. MB shop wants $1600.00 to replace the whole left exhaust system! So far, I've not done anything.