Below is a photo of my Shimano rear derailler cable after approx. 5,000 miles use. I haven't been in cycling long enough to know, but my mechanic was appalled! My shifters are Shimano 6800 series (on a Spec. Roubaix). The mech. even contacted Shimano to ask about getting me a new shifter; he feels that there is a design flaw of some sort that results in the shifter "chewing up" cables like that. No-go on replacement from Shimano, but I am very glad to know what to check on when my usually flawless shifting goes haywire. Anyone have similar experience?