The rear wiper on my 240 Wagon does not function on intermittent setting - it moves only a little bi when it is supposed to sweep. The regular and high speed settings work. Howeve, on intermittant and regular settings, the wiper arm does not return to the normal down position automatically. Is this likely the motor, the switch, or the relay? Is removing and replacing the wier motor and linkage assembly from the rear door difficult to do? Thanks for any help!