Hello. So, my sister's Whirlpool washer stopped agitating (the agitator does not turn at all) and the tub will not spin. Neither of these parts have any motion but it will drain out and you can hear the motor working. It makes a horrible grinding sound during any wash, spin, or rinse cycles.

I checked the motor coupling. The black rubber piece appears intact. It is not cracked or degraded. The two plastic pieces are whole. Neither is cracked or broken.
I also looked at the clutch assembly. It looks like the one shown on the website, only older. I could see no signs of damage. Though I admit I am not sure what to look for.

The motor coupling turned smoothly when I manually turned the motor shaft. The clutch assembly turned with the motor and motor coupling.
The basket drive did not turn when I manually turned the motor and clutch assembly. I do not know if it was supposed to.

The transmission does not appear to be cracked or damaged from an external evaluation. There is no leaking oil. The outside of the transmission is rusty, but other than that seems fine.

I am not sure what is causing the problem at this point. Would it be the basket drive or the transmission?
Is there anything else I should be looking for that I might be missing?