Saldous,

I use Swain & Jones in Farnham. Their Service Manager is called Alan Barlow. He seems to know a bit about their range of cars. I haven't needed to test his knowledge on the XF, but if you want to give him a call, his number is 01252 747447.

I think that you should get your sills working without resorting to a replacement set. They do not seem to be faulty. Sounds like the dealer is simply trying to shift responsibility for fixing the problem. I reckon that the new set will have the same issue. I could be interested if you do end up with a spare set.