92 500 SL Windshield Wiper problem

My windshield wiper stops in random places during use, especially when on intermittent. It stops in the middle, all the way to the passenger side, or anywhere in between. When on low, it works OK, but when I
turn it to off, it sometimes parks in the middle of it's stroke, instead of going back to the parking position.
Would this be a wiper relay problem, or am I possibly looking at a motor problem?
Thanks, Steve

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