I get MPG's in the low 20's with my '85 300D CA model and that is combined driving with a very heavy foot. I still have to original sticker as well (curiously two of them) and it states ONLY 21 and 22 for the EPA ratings.
The worst I've gotten was 20 mpg's and 25 as the best. This is a car with over 200K miles on it. Even the previous owner said he got around 20 mpg's from my car. If I plan on keeping this car for a long time, I'm thinking of getting rid of the oxidation catalyst and converting it to a federal intake/exhaust set up as I would imagine the CA set up robs fuel economy in addition to HP.
Another interesting thing I've read from a 1982 Consumer Guide book is that in 1982, the 4-speed automatic replaced the 3-speed automatic as standard equipment in the 300's. They also switched to a 3.07 rear axle. So I guess everything before 1982 that had automatics were 3-speeds. Is this correct?