I would get the parts for the Panther G from Karen and see if it can be upgraded. Since I have built my Pershing it has become my main fighter so i will need to address this some time in the future so I am going to try it.
For now i would think that you could simply get a card sheet of Polystyrene from a hobby shop and make a plate the same shape as the under side of the turret that the ball bearings ride on an basically have a big patch panel. Now the bearings are riding on a new flat surface just like in the beginning.. Makes sense doesn't it?
This also will bring the turret up off of the lower deck to give you more clearance.