111R heater air flow distributer

[106500]

Anyone had one of these fail - the air is blowing on the face vents and movement of the knob changes nothing. I understand that there is an electric distribution motor which can fail particularly as its prone to getting wet. However my 2004 Elise has rarely been driven in the wet and is always garaged. Obviously I want to pinpoint the fault if possible as I understand that to replace the motor requires clam shell removal. Anyone had this problem?