Friction in Janus C aileron control

The Janus C I'm flying has a lot of friction in the aileron control,
when it gets cold. I've been through all the linkages in the fuselage,
and none are likely suspects. In the desert heat, before takeoff and
on tow, the ailerons work smoothly and easily, with very little
friction (feels about like the club LS4). Once up at altitude, where
it gets cold, the friction increases dramatically. If I land and wait
a few minutes for it to warm up, it becomes nearly friction free
again. I orignally thought it was the bending of the wings, but this
weekend I noted the difference was very strongly correlated with
temperature.
Anybody else have this experience?