Calculate, rather than measure, mileage by dividing distance travelled by amount of fuel to fill-up. It's best to do this over time to smooth out differences in temperature, how full it actually gets, etc.

Folks post a personal best 35mpg in a 560SEL. I suspect the fill up just after netted 10mpg with the same driving. The difference is attributable to not quite filling up to the top for that 35mpg run giving the impression of having used less fuel, or fuel vending equipment set by unscrupulous vendors.

A quart in 1700 miles doesn't seem drastic. Particuarly at 70-75mph when the M103 is turning over 3500rpm. M103s are known to consume more oil at high rpm. Consumer Reports' article on the 300E in 1986 noted that it's probably a design feature that the engine ingests oil at high rpm. I take that for the observation more than logic.

Sixto
95 S420
87 300SDL