Am I missing something. The wiper motor is covered by the dealer that fixed it, Lesters, but you want another dealer or warranty service to pay for the repair. Shouldn't it be Lesters' responsibility or the motor manufacturer's responsibility to authorize out of area repair? I'm not sure GS is using "any excuse" not to pay a claim, rather they are using the specific excuse that it is covered under an existing warranty. I totally understand your frustration, it is just that it may be misdirected...then again maybe not.
Hope it all works out, and Happy Trails.