1999 Adventurer Windshield wiper issue

During our first trip to southern Florida, we passed through a rainstorm, & during this part of the trip when I had the wipers set on delay setting, the stopping point would vary randomly. :h

Normally the stopping point is at the center post in the windshield. Any one have this happen to them & what repairs are needed? :?

It's not a major problem as I can keep moving the wipers until they stop out of my field of view...