I doubt that a car with 177,000 miles still has a trap oxidizer. It has probably been replaced with the trap catalyst which, on a W123, is identical to the trap oxidizer, and is supposed to be a lifetime part. As Diseasal suggested, however, it’s probably full of soot and replacing it with a bypass pipe would be a good idea if your state doesn’t have strict emissions inspections for old diesels.

Congratulations on your purchase and I hope you have fun working on the car. I’ve always found this forum to be very helpful and responsive.

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Christopher
'06 Mercedes E350 station wagon (silver/black)
'85 Mercedes 300D (black pearl/palomino)
'85 Mercedes 300SD (smoke silver/burgundy)
'79 Cadillac Sedan DeVille

'05 Toyota Camry (because always running is nice)

'85 Mercedes 300D sold back to orig. owner 8-1-06
'84 Volvo 264GL Diesel, owned 2000-2013