It looks like the discharge pipe from the coolant pump, if it is then it's exactly where your leg will naturally sit while riding your bike. You must be rubbing away at it without noticing. Can't say I've ever noticed how close that pipe is to my leg while riding but I can't think of any other logical explanation.
Went for a blast at the weekend and confirmed that mine is doing the same after only a couple of hundred miles (it's a new engine). Pretty crap design TBH. Looks like i'll be buying Samco hoses as well.
