Do you know how to disable the touch screen? I also never use it and just use the buttons.From the first post you can clearly tell this is a touch screen issue and not a CMU. As others had said, it only acts up when sitting still because that is the only time the Touch screen is allowed to talk to the CMU.
The question is can you fix the touch screen and chances are you can't unless you are lucky enough that some dirt or buildup inside is applying pressure. Most likely the real fix will be to replaced the touchscreen. The work around would be to see if you can permanently disable the touch screen (sort of like the hack but in reverse).
Personally I find that I never use the touch screen. Most of the time I need it is when I'm moving and since it doesn't work, I have learned to use the controls so much that when I'm sitting still, I forget I have a touch screen all together... (maybe the lack of use will make it last longer) Between the controls, steering wheel, and voice.... I find the touch screen is only really helpful when typing in an address for Nav.
Good luck...and don't let the crappy dealer talk you into replacing the $800 CMU.