So I currently have an Audi A3 (8P) 2010. I've only had it for 3-4 months but recently my rear wiper has been totally out of control. It would start to turn on even when I have it on the 'off' position and start behaving erratically. Recently it's been getting stuck halfway up the rear windscreen (pointing upwards). And it won't move even when I turn my dial to the 'on' position or keep switching between on and off. I've had to get out of the car and readjust my rear wiper manually by moving it inches left or right and then turning off and turning on the car again for it to work. Just yesterday, I had to readjust my rear wiper to make it move for it to then continuously work non-stop for 5 minutes and the only way for me to turn it off was for me to turn the ignition off. Currently it's stuck halfway up the rear windscreen again and every time now I turn the car on it's making a really loud whirring noise as if the thing is about to blow up.
From looking at forums it looks like an issue with the rear wiper motor but how can I be so sure that this is the issue?
I called up two different mechanics to get a quote to fix this. One mechanic told me straightaway that the issue is with the rear wiper motor and quoted me £300 for the job (£185 for the rear wiper motor and £115 for the labour). Another mechanic told me he's not sure what the issue is and quoted me £70 just for the diagnostic charge.
Do you think it's better to just go to Audi themselves since £300 sounds about the same price they would charge as well unless I am wrong?