How do I know if the problem is with brushes versus motor?

Whirlpool ultimate care II. After reading many Q&A's the carbon brushes sound like the place to start looking. How do I know for sure it is brushes instead of motor. It was at the end of the cycle the water pumped out but it didn't do the final spin. It still pumps water in and when it trys to spin makes a loud noise. When looking in it seems the tub is not tight. The coupler piece appears in tack and I can manually turn it?
PS wirecutter you seem so wise please help