I "think" my 97 C280 ( M104 inline 6 ) is in the 23 + range but haven't checked lately. And the windshield is out for a replacement / headliner recover so it will be a bit until I finish the tank and get a #.

I'm somewhat partial to the 97, is it is the first year for 722.6 electronic shift 5 speed, last year for an actual metal key / M104 inline 6 .

The 94 - 5 - 6 would be OK also with the only real difference being a hydraulic shift 4 speed auto.

I don't know that fuel mileage is such a major issue when selecting an older used car. I sure would not pay a huge amount extra for better mileage if a otherwise good car could be had for less $ and use the difference to buy a bit more fuel.