I would first try some rubber dressing/protectant on the channels to
see if that helps.
I took some 303 Aerospace protectant and lubed mine using Q-tips and
they run very
smoothly now. Lower the windows, load up the Q-tip, and have a go.
Make sure you "squeeze"
it into the corner where the window and channel meet, so it runs down
and lubes the part of the channel
inside the door. May prevent you from a lot more work and cost! :)