Does your 190D have the 2.2 four cyl. engine, or the 2.5 five cyl. engine?
I remember the 2.2 190D 5 spd was listed as getting 52 mpg hwy when new, don't remember the city rate. This is from the same reference that gave the rates I cited before. Don't remember the publication, but it was in a MB shop specializing in older MB's.
There is a guy here with a gray market 86 190D 5 cyl with 5 spd manual tranny, he put in a different rear end with higher gears, and claims to have gotten into 50 mpg as his best to date, gets regularly in the mid to high 40's. Unfortunately the body is quite rusty. Maybe it's significantly lighter because of it!
Bob