How to enhance your reputation - a short story

I took our B-Class Mercedes to the local dealer in Stockport, not once but three times in the past month. The vehicle developed a clunking noise under the bonnet. It's 3 1/2 years old and I had bought what proved to be a useless extended warranty from Warranty Direct. It took the mechanics at Mercedes Benz in Stockport three attempts to discover the cause of the noise. This wasn't their fault, it was down to that strange phenomenon where you take your car to the garage, report a fault, and then they can't hear or find anything! Things like this happen to me all the time - I make an appointment to go to the dentist, and by the time I get there my toothache's gone!
The car ultimately had new shock absorber mountings fitted and is now running smoothly again.
Well done to the receptionist, service manager and mechanics at MB Stockport. They welcomed me, took out my car to listen/experience the (sporadic) noise, found the cause and replaced the parts.
The main point of this story is yet to come: I was invoiced over £600 for the job, and duly contacted my warranty people. Then I was told this specific problem wasn't covered (although of course you don't find out what the problem is until half the engine's out of the bonnet and the mechanics need to put it all back together again). I raised the point with Mercedes Stockport, whose manager there contacted the powers that be at MB head office, wherever that is. They agreed that because of the low mileage (36000 after 3 1/2 years) that the fee would be reduced by a good 60%.
The reputation of the dealer in Stockport and Mercedes Benz UK in general has been enhanced. They obviously need to sell the benefits of their extended warranty product more strongly. Price isn't everything, and a layman like me doesn't understand the implications of 'mountings' not being covered in a cheaper policy.
Roger