As Toad said, I think that this problem is likely to be stiffness in the rubbers on the sides and bottom of the window. Electrical problems, such as rosin rot or damp PCB's are unlikely to cause such a specific set of problem descriptions. Note that everybody has a similar problem!
Silicon spray worked wonders for mine, it needed quite a few treatments, but even 1.5 years later, it's still OK.
The window works by detecting an over-load on the winder motor, and this serves two purposes, to stop when the glass reaches either the begining or the end of the it's run and to prevent it from choking/catching heads and fingers of small individuals.
When the window is cold or wet, the resistance to rolling the window increases at a point, and the motor overloads and cuts out. A good way of determining this is to observe what happens on the open and close operations... During open, the motor cuts out less then when closing as the weight of the window causes additional stress/weight on the unit.
Try (re-)applying Halfords Rubber lube to all of the seal rubbers on the window. Excercise the window afterwards, and you should see an improvement.
Flux cleaner can be used to clean the PCB if required, and a good PCB sealant (or potting compound) can be used to insulate it later.
Let us know if this resolves it?