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

I have several 2620's and like them a lot.
One that I use will not hold a display screen calibration. The touch points can be off up to 1/4" on a day to day basis. I usually have to do a display "calibration" routine to get it set correctly. Is this a known problem and is there a way to fix this without it having to go back through Garmin's service center...? Thanks for any help.
Skywagon185