well you made the fatal error of using AC glad you didnt trust them and got a second opinion
Arnold Shark = twunts
Wee story for you - my first car an Astra..........driving up to Pitlochry .....BIG bang everything dead- (pretty scary when you were burling along quite happily)
Belt had snapped .....result= engine shafted.
Towed to Arnolds - turns out belt wasn't replaced at the previous servvice when it should have been. Three weeks of wrangling with them and Vauxhaull - end result a new engine at their expense Service manager thanked me for business and sincerely hoped he would never see me again...........he hasn't and I've had two vauxhalls and a nissan since not from them and never ever serviced by them.