Hello. My name is***** can help you with your question.
This sounds like the motor is failing. The motor controller board is a more common problem, but based on the symptoms you are having is almost definitely the motor. The only way to test the motor is to open it up and put 12 to 18 V on the leads and see if it moves at a steady pace. It would be somewhat difficult to test the load on the motor without actually replacing it. There is a replacement motor available and I'll give you a link to it here:
Let me know if that answers your question or if you need additional information.
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