Maybe you descend like a maniac and never use the brakes. Maybe you live on Antarctica and so don't have to deal with hills or stoplights. Whatever the case, if your baking is still pristine but your shifting is getting muddy, you can replace just the latter with Jagwire's Road Elite Sealed Shift Cable Kit. While it downplays the occasionally loud aesthetics of other Jagwire kits, the Elite Cable Kit still features the slick operation of polymer-coated cables and Speed-Lube housing.
Jagwire recommends this kit for Shimano and SRAM road drivetrains only — Campy-philes need not apply.