Hi,
Just because the bike is 4 years old it dosn't mean the dealer can wash their hands and walk away from it. You still have consumer protection that lasts for 6 years. It obviously depends on the condition of the bike the milage and if its been abused, but these thing are supposed to be tough and are advertised as such. It sounds like there was a fault in the manufacture or in the metal used from new.
The responsibility is with the dealer not the manufactured, so put this to them in a reasonable manner refering to the quote below, which is taken from the Office of Fair Trading website, "a guide to customers rights for retailers". If you don't get anywhere then have a word with the OFT.
Offer to pay for the parts if they will fit them at their expense, that would be a win win situation without both parties having to involve further cost with the OFT and legal advice etc.
" QUOTE from OFT website;- Customers' rights last for six years
The law says that a customer can approach you with a claim about an item they purchased from you for up to six years from the date of sale (five years after discovery of the problem in Scotland).
This does not mean that everything you sell has to last six years from the date of purchase! It is the time limit for the customer to make a claim about an item. During this period, you are legally required to deal with a customer who claims that their item does not conform to contract (is faulty ) and you must decide what would be the reasonable amount of time to expect the goods to last. A customer cannot hold you responsible for fair wear and tear .
The six-year period is not the same as a guarantee, but it does mean that even where the guarantee or warranty supplied with the product has ended, your customer may still have legal rights."
Worth a try. Good luck.
OC