I can't tell how big that filter is. The 140 filter that fits over the the blower motor, at least a 140 without activated charcoal filter, is about a square foot in area and looks like the before picture in 5-6000 miles of driving around the San Jose area. The 140 has an additional recirc filter about 20 square inches in area under the glove box. That one lasts longer.

Jeremy, does the 210 not have a recirc filter or does the filter in your picture handle fresh and recirculated air?

I found a shop in Japan that sells retrofit cabin air filters for early 124s. It fits over the blower motor intakes. It was something like $80 before the crazy run in exchange rates so I don't know what it costs now. I can't find the name of the shop Unfortunately the cabin air filters from 94-95 124s will not fit. Maybe if the whole blower motor intake plenum is swapped...

Sixto
87 300D