Adding to my last post, I rem'd having replaced a wiper motor in a 94 much time ago, and I'll be kicked if I didn't find the junked piece sitting on a shelf in the shed..lol
A quick test reminded me that the wipers went from stalling on the winshield at intermittent or low speed, and would only reactivate when the the hi-speed section of the circuit was engaged. Symptoms of impending complete failure (iirc), were grinding noises caused by the internal cog assy slipping, when the crowns were worn badly. Sounded like a thurrrump-thurrump, and progressed to a continuous vibrating grind. Theres a centre shaft that could be the culprit if it has too much longitudal play; which would effectively allow the cogs to ride above/below the norm position.