Warranty is dead, did you buy from Norton or a Dealer as that matters.
Norton, pay or diy, depends on whether the dealer stamp in the book has any value if or when you come to sell.
Dealer, no manufacturer warranty but consumer law says the goods must work for a reasonable amount of time so the dealer has a legal duty to cover faults, having the dealer do the service does not give them the excuse you caused the fault by badly servicing the bike and not cover any faults.