Does my car have a climate control problem?
 

To air condition my car, I used to set the climate control to 75, fan to auto, forget it, and stay comfortable during the summer. Now 75 either freezes me out or is too hot. I often have to move the selector to 80 or 70 to stay comfortable. The temperature is still regulated, I'm comfortable at the new setting, but the set point is all over the place each time. Is this a precursor to a serious problem?

Sounds like an interior tempature sensor going bad. I'm not as familiar with your chassis but with the W123 / W126 there is a hose that pulls air through the temp sensor that falls apart. Your vehicle may have a similar set-up in a different location.

My Volvo acted the same way when I had the interior temp sensor covered up, taped to the roof while doing the headliner.

The sensor is in the header above the rearview mirror. I remember cleaning it a few years ago. I'll have to check it again.