Some dealers will make you wait until the trap oxidizer is plugged or otherwise failed before replacing it. No problem (other than the crappy performace you get first!) as they will then have to replace the turbo and exhaust --- you get a new downpipe anyway as it has a trap catalyst in it.

If it whistles or has bad performance (0-60 in more than 14 sec) it's plugged.

Peter

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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!