This is the same car with the unconnected O2 sensor?

Replace sensor and verify that is it working properly -- if it is way off, it will cause intermittant lean running (or rich, but that won't cause you any performance loss!).

Cat may be melted if it was running too rich....

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!