replace wiper motor

This could be indicative to a wiper linkage / transmission issue that requires a physical inspection.

first see if the nut is loose where wiper arm attaches to the wiper transmission, should be 13mm socket there is a plastic cover over the nut use a pocket screwdriver to remove then you can access the nut. if it is tight you would need to remove the cowl panel to inspect the wiper transmission for damage or breakage