I'd suggest buying a different chassis with the separate 2028-100 motor and truck. Something like this: (please remove link if not allowed) https://www.ebay.com/itm/LIONE...0:g:dkAAAOSwOIlb9Ehk
This is the setup used on all Postwar and the later "high end" MPC/LTI/LLC GP7/GP9s. It's stronger, more durable, and smoother running that the setup your GP7 has. I avoid that combination motor/truck like the plague. Just put your current shell on a new chassis and enjoy.