I’d inspect and lube everything you can get to in the aileron control system. If the wings bow up in flight, duplicate the bow by raising the wing tips. Something else I’d try is to make the stick taller which will give you more mechanical advantage...........I know a major manufacturer that did this to help out with higher stick forces in the air. When flying fast, hold on to the stick up on top, down low when thermalling. Can’t recommend re-doing the control system as this would involve major surgery to the wing and ailerons and would change the balance of the ailerons, also. Doubt that adding Mylar seals would help stick forces.
Hope this helps,
JJ