Im having the exact same problem with my W plate 206GTI. Dealer has said around £200 for fitting a near side front actuator (scratch that!!)
Have tried checking the wiring looms for bare wires that could be earthing, but all looks pretty good inside both doors.
I can get an actuator myself for about £80, but I dont know if trust the dude at the garage enough to buy it (he spent about 5 mins with the car and was about as helpful as a hole in the head)
Will try the WD40 in every orifice technique and see if I have any joy.
Andy - did you get your car fixed in the end?
Cheers - Mark D
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