Bought an A5 with 20,000klm on clock but had to top up with a litre of oil after one week of driving. The guy I bought the car from said these things happen from time to time. Eventually I took in for service at 30,000klm to an independent mechanic for a review and he advised that the sump thread had been stripped by previous 15,000 klm service. Oil leaked everywhere over the floor pan evidencing the leak had happened over time since my purchase. Took back to the prestige car dealer to ask how this could have passed the high standards of car care they offer. His response was it had been checked and all ok'd and that I would get a refund for the helecoil repair in my next service. He also offered to buy the car back off for me for todays market rate - gee thanks for the great deal -NOT! I asked for the sump to be replaced and the car to be returned in the condition that it was sold - he said no and basically flicked me. I am soliciting thoughts on what to do here and how I should approach this further.