brucelee wrote:Also does anyone think I could blag a warranty replacement ?
Definitely. And not under warranty. Sale of Goods Act trumps warranty, and under that any failure occurring within 6 months of purchase is assumed by default to be inherent, not the fault of the user. Go back to the shop and demand a replacement KMC joining link. They come in a pack of two (why? because they fail sometimes of course) so then you'll have a spare.
It shouldn't be hard to persuade the retailer that it'll be much less trouble simply to hand over the pack than go to court and try to convince a judge that you abused the bike by fitting those 'upgrade' pulleys - that won't have made one jot of a difference by the way.