Thanks guys, the motors are good, in fact I got one rebuilt.
And the channels certainly look good, likewise the rollers, all in good shape and lubed.
Both windows ONLY stick when fully up, it's like they've become wedged into the small guide at the top of the channel that runs up the division bar. (Between the main window and the 1/4 window.)
When the mounting bolts are loosened off and the pressure comes off the window it allows the window to 'drop' 1/16th of an inch and it works immediately when I work the switch.. After tightening the bolts all is good for 4 months..or 7 months...or for a year.
There is no sign of a tight spot or similar when the winows roll up and down, it's almost like the motor just can't break the window free from this wedged situation.
A Thunderbirder from the Land of the Long White Cloud.