No belt in yours, it's cable driven.
Just the motor/gear drive:
The window glass could be binding in the fuzzy tracks.
The window "carrier" could be binding in the vertical regulator guide.
The idler wheels at the end of the regulator could be siezed.
The drive cable could be frayed.
The gear drive could be stripped or binding.
The motor itself could be getting "tired", worn brushes or bearings.
Since you have to take the whole regulator and motor out anyway, it's
usually more time and cost-effective to just replace the whole assembly.
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