Ever check the transmission fluid level since purchasing? You very well may have. Yet this can be the result of not bothering on a very old car. It also can just be wear. Not typical
at 190k miles though.

This transmission was also used behind the brands large V8s at the time. So the design is not weak. Personally I would just look for a used replacement. Depending on the year there are two examples. One is cast iron and the other aluminium. I would replace it with the one currently in place.

Sometimes the nut on the yoke can become loose. That does not sound like your issue. At least used examples can be found still. My guess and it is only that is you have lost a shaft bearing.