How do I replace the heater motor bearing/bush on my 2007 XTrail?

My XTrail heater fan makes a loud humming sound which usually starts on a RH corner or roundabout. I used to be able to stop it by turning the fan off and then on again or turning it up to max and then back down. Now I just have to turn it off all together as it hums most of the time.
There seem to be many references to this problem and my Nissan dealer wants over 700Euros to fix it. Does anyone have the part number(s) of the bushes or bearings, or does the whole motor need to be replaced?