You must remove the shell and then remove the motormount from the chassis and the power truck. This "usually" involves removing 4 screws.
I normally try to raise the motor out of the gearbox just enough to shoot some grease in there with a syringe. The motor need not come completely out of the loco.
It's tedious, but not impossible with some patience. Pay close attention to how things go together as you disassemble.