It sounds like the temperature dial wheel is not 'aligned' with the thermal element it activates.
This is the way I think it works. I could be all wet, and am not an MB tech, but here goes.
As you turn the wheel to warmer or cooler it mechanically moves the on/off point. From what you describe, 75=65, 90=80, the dial 'reads' 10 degrees off from the element setting. Now, if that is so, I don't know if there is a mechanical adjustment to re-calibrate the dial or not.
How new/recent is the rebuild on the climate control pushbutton assembly? Perhaps it wasn't properly calibrated during rebuild. Try talking to the supplier of the rebuilt control, tell them it's 10 degrees off everywhere and see if they offer to re-calibrate it for you.
Good luck and BCingU, Jim