The trap oxidizer looks like a big metal can, on the passenger side of your engine. If it has been replaced, there will be a tube that looks like it is wrapped in foil.
I am pretty sure most cars by now have that recall work done, althogh the 87 I bought this summer still had one

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Dan
2005 E320 CDI - 246k
1987 300SDL TD05-16g, Herlevi pump, Elbe manifold, 2.47 LSD - 213k
Past: 1987 300D - 264k