Garmin 2620 with a touch screen display 'drift' problem...

Woofer....
I have several 2620's and like them. One unit is giving "touch" screen problems. Using the normal 'Find' steps to touch calibrate the screen, it will not hold its calibration. It can be off 1/8" - 1/4" to the touch. Not good when naming wpts,, etc. It does not seem to care if the unit is hot or cold. It still drifts on a daily basis. The error is always on the right side of the screen and it can drift either + or -. There have been times when the upper right "Close/Back" button is always there, but not accessible to the touch as the drift has its ghost clear off the right hand side of the screen. Usually the drift is the opposite direction.
Any suggestions on how to fix this screen drift problem.