Rear glass hatch problem

I have have 1997 Blazer LT and my rear hatch release button (for upper glass door) works only about 5% of the time. (Either inside release button or pushing the outside button) It seems to work only when it has not rained in days or I do not drive my vehicle for days (after stored in garage). Most of the time when it does work, it only works one time.

Anyone having this problem?? Please help.

replace the unit in the tailgate?