What is the best way to calculate how much a second hand car will depreciate over a certain period of ownership? I ask as I have an Oct 06 Golf 2.0 TDi, which, after reading your review on their potential problems I will consider buying a series of aftermarket warranties for. However, after seeing your review on the Audi A1 diesel where you say it should retain 66% of its value after three years I wonder if buying new might not be so expensive after all as it will of course have a manufacturer's warranty. Understanding how the Golf will depreciate will help me make my decision. On the subject of buying new, is there a source of information somewhere that will give expected retained value after three years on all new cars?