We purchased a Mercedes S500 in May 2006, which has now done 20,000 miles. It has been regularly serviced by Mercedes Benz Stockport. In May 2009 I was invited to have the car checked for any potential warranty work and an MOT. Being cynical I was of no doubt this was to drum up business for the main agent. On June 12th the air-conditioning failed. I was told that a drainage hole under the bonnet had become blocked with leaves and as a result water had damaged the air-conditioning unit, costing around a £1,000 to rectify. I contacted both the garage and Mercedes Benz in Milton Keynes. I felt aggrieved as the car was just out of warranty, had been checked a few weeks earlier, no mention was made in the service manual to clean this drainage hole and on the Internet several other owners had similar problems. This is clearly a design fault. No reimbursement part or whole was offered and I was told that my only course of action was to contact the ombudsman. Have you any suggestions? Readers beware Mercedes customer service is not what it was.