wtf, there are some pr!cks about aren't there. this, for example:
With a crank that worn I wouldnt even have thought about warranty let alone starting a thread on a forum about it
off the back of this thread i actually went home and took a closer look at the profile of the crank and compared to the drive side which is a lot less worn (still got SLX logo). the shape of the worn one is considerably different - i'll try and post a picture or two later on if i can be bothered, but it's quite obvious that the metal has worn down from heel rub.
so therefore this thread has highlighted the fact that i appear to have one spaz foot and the crack is almost certainly down to excessive wear and i'll probably not waste any more of Robz/alpine bikes/shimano warranty dept's time trying to pursue a claim of sorts.
for the record i'm not some naive fool who thinks things don't wear and break (should see my spares bin) - i just spotted the crack on what i considered to be a solid component on my bike, was a bit concerned that it might have ended in tears if i hadn't spotted it and came on here to seek like-minded opinions on what to do/the cause. is that not what forums are for?
so anyway, i'll be helitaping my XTs and searching for a spare non-drive SLX if anyone's got one lying around (don't expect Robz to offer anything constructive).

