My SL55 won't start when it's cold - it doesn't even recognise there's a key in the ignition.

I called out a Mercedes specialist (used to work for Mercedes), who was very quick to diagnose the problem as he said it was not uncommon. Apparently, the soldered connections on Mercedes' ignitions are unreliable in the cold. His solution was to warm up the ignition with a hair dryer, and hey presto, after a couple of minutes the car started.

I called up Mercedes-Benz customer service, who didn't want to know (other than to take my money for a diagnostic check and then charge me for the solution!).

I suppose my question is: Do I have any comeback against Mercedes? Surely they can't sell cars that only work above, say, 10C? Is this covered by the fit for purpose law?

The car is a used car, not bought from a Mercedes dealer, and the problem appeared after 2 years trouble free use.