Hi Guys

My friend is fortunate enough to own a C class with the 3.2 engine. He has done about 160,000 km and has just experienced loss of power due to a blocked catalytic converter.

I know that this happens if fuel is contaminated in some way. Can somebody please elaborate on this. Is this contamination of unleaded with leaded fuel? Is this a long term process from poor quality fuels ? What can one do to avoid this problem ? Will this sort of thing happen anyway and are cats required to be changed after a certain mileage ?