Just had that problem... The motor was fine. It was the main assembly with the pivots that were seized up. I bought linkages also just in case, they were a mere $7 CAD each at the dealer, while the wiper base assembly was $116 CAD. It solved my slow wipers...
Oh yeah, just to clarify, The linkages will rarely seize since the linkages have plastic joint receptacles. They would wear through, not seize. Get the wiper base, and about 1/2 hour of work... it's really easy to change. The hardest part was getting the wiper arms off the pivots, but a bit of liquid wrench or release-all soaked in will make it easier.
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