I bought a replacement coupler from Appliance Parts Pros. The part that arrived didn’t fit quite right when I tried to install it. It wasn’t fitting all the way down the drive shaft. This was because of a cam sticking out of the replacement part that didn’t exist on the original part. This cam was hanging up on the opening in the floor of the microwave that led to the turntable drive shaft. This was remedied easily with a diagonal pliers. Now everything is working correctly.