Power windows

left rear window goes down normally but struggels to go up without help. Dont detect any binding and it is going straight. Would it likely be the motor or regulator.

Lower the window and spray silicone lube into the both window channels at the base of the window opening. If that doesn’t work, you may need a new motor/regulator.

I agree with jtsanders. Start with clean/lube and then see how it operates.