Starting Saturday my wiper would never stop. Today the boot was indicating open and the alarm was going off intermittently. Was exactly this issue - switch was in fact frozen up with water from a leaking motor.
latta1989 - you don't need to remove the lock. I used a small screwdriver to pop the microswitch connector off the top and just squirted it with some WD40. Seems to have done the trick for now.
The water on my motor is leaking out from around the silver lid. Does anyone know if it's possible to repair the leak within the motor? Or is it simply a case of replacing the whole unit?
Thanks for the great advice on this thread.