I have a simular experience, though not job/retirement wise. I use my '81 240D MT for a work car. I get 27 to 28 mpg. This is basically, country roads. I drive roughly 15 miles each way. I did drop to 27 mpg, but recently replaced the air cleaner.
I did notice about 32 mpg, when I did a tank full of highway driving at about 55 mph to 65 mph. That was only one tank full though. On another tankfull, I got 28 mpg doing about 70 mph.
I haven't calibrated my Odometer with highway milage markers. A GPS would do the same thing.
Tom