I will install a new motor coupler, put the machine back together and give her a whirl.
While I'm thinking of it, I have a habit (an OCD type thing) of spinning the agitator a few times, by hand, with detergent in it and as the tub is filling. I do this to dissolve the detergent more quickly so I can then put the clothes in before the tub is completely filled. Am I messing with the transmission by doing this, and could this action caused the coupler to fail?
Again, thank you for prompt, helpful, and professional assistance.