When I bought a new engine air filter the parts person asked if I also wanted to buy the cabin filters. I passed on the cabin filters because I wanted to first inspect them - but I can't seem to locate them on my car - where are they hiding? 1986 300E W124

Apparently pre 1994 Mercedes do not have cabin air filters.

Located the cabin air inlets which are under the hood by the windshield wipers. By looking at them it seems to me that if one had to have cabin filters, the inside of a home furnace filter cut to size and clipped on top of the inlets would do the job. This would be very inexpensive and super easy to replace when required.