As has been said earlier, a "full warranty" has many exclusions. You should demand the warranty documentation from the supplying dealer, and check for yourself instead of making assumptions. If the warranty is a SEAT warranty you might not even have to take the car back to the supplying dealer. You should also check that any inspection they should carry out before delivery, if it is supposed to cover the parts involved, was done. You might have more luck getting at them for not doing the checks properly, rather than the warranty.
"Local seat" can say what they like, but they're not the ones going to repair it, are they? If it's a SEAT warranty, have you checked that they can't do the repair if they're such stars? At least their opinion might
help if, as above, you're suggesting the pre-sales checks weren't carried out correctly.