Does the patio wall come into contact with your garage? If there is a gap the patio wall probably doesn't have much to do with the moisture. Does water pool up between the two? I would be concerned about drainage You would eventually have wood rot on the exterior siding if there is inadequate drainage, then rot at the sill plate, then rot at the base of the studs.

Im wondering if you have a roof or siding slow leak. Even just an ounce of water in a slow drip can cause the circumstance that you mention.