Just to echo: Wear items are not normally covered. I just renewed my warranty. List would have been £2k. I paid about half that direct from Warrantywise, but £400 seems *very* cheap, although since you get a 6 month warranty (effectively) from a dealer, maybe it's only the extension.
If you want the car and you're happy with everything else, just make sure you've got £3k in the bank and drive it until it does a MAF.
C