Jim B+ have you checked to see if the differentials are the same in those 240D's?
I doubt that an automatic would be happy if the same gear ratio in the rear end as that manual. The car with the manual tranny ought to run at 80 MPH without stain compared to the one with automatic. The ratios could be different. Look at the left lower corner of the gear case where its stamped into the casting. I believe the factory gears are 1:3.69

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!