See if some one can try adjusting your mixture a touch richer but cat may be toast.going with a slight mixture adjust ,either way may drop the hcs.My experiance with MB'S (and bmws)
is alot of aftermarkets cats last 2 years.on my car this is the case.Even the shop i use to put a new cat on says to smog the same day.The only thing that may save you is you are not on a dyno measuring nox .you may find someone to get your mix to pass.
Your car has a 3 wire 02.This part MUST be direct fit AND BOSCH.and pretty new.I work as a smog repair person and do a lot of 02's.As your co is not terrible 02 may be working ok.
A little ,slight adjust,toward rich may drop your hc's alot.
Rich

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88 300E White, sold 9-04
88 190E Black 2.3 sold
90 300CE White, Grey sold 12-24-04
92 400E White,Grey Sold 5-06
90 300CE 91K Signal Red,Black Sold 2007
1989 300CE Smoke silver,Tan Sold 1-08
1993 300E 3.2 M104 motor
1991 300CE White,Grey
1994 E420 beautiful car,gone to new home
1994 E320 Smoke an Parchment.Beautiful car