@dc42
The drivers are set to 1500mA (12v) and while the drivers could take more I am not comfortable running the motor at much more.

I suspect the real cause of the problem is the 8mm Y transfer axel instead of the 5mm that is usually used and the Iglidur G bearings don't like the kind of transverse load that the bands put it under.
I hope to be able to replace the Iglidur with roller bearings soon as that will likely solve the problem for real.