Trans trouble

I have been having a vibration issue for a couple of years.. tried everything..

This weekend, I went to triple check the u joints and found I could move the shaft that exits the transmission (904)... probably by close to a 1 /4 inch in all directions..

There are very small flecks of metal on the splines.. the yoke seems to be loose on the shaft when installed( some back and forth movement when turning it with Trans in gear..

I am presuming the shaft should not move..
Is this repairable or is a different transmission in my future..

And Is the a500 the same external size as the 904?( if I have to replace this one.

Thanks for your help.