Originally Posted by djb;[url=tel:23675032

23675032[/url]]thigh-- have seen you over on the touring section.
Curious--does one brifter shift up and the other side down?
Is the worn side for upshifts?

specifically about tension--Ive had this happen on my spd era shimano Tiagra brifters, but I also noticed that in my case, it has been worse when slight derailleur adjustments were off a bit, making more tension for cable, increasing tension at this crucial bend point, and this tipped the balance for increased wear.
Once I figured this out, I've had much better cable life happen.

I don't know if a pinion setup can be slightly misadjusted and cause more cable pull tension that is really needed? Perhaps look into this.
I also very strongly second or thirdly suggest inspecting more often. With a rd, in hindsight I also realized that I had been ignoring clues, ie rear shifting getting a bit sloppy and then having to do a teeny tiny barrel adjuster turn to remedy -- this was the very start of fraying. I've been lucky and have been able to remove the frayed bits easily to replace.

I wonder also about your housing, it is full length like on my tough touring bike, a Surly Troll set up with Genevalle shifters (look them up) and full length housings can have more friction also, so what about tri flow or silicone stuff in the housings?
You should be able to get a feel for the force needed to move your left shifter and see if you can noticeably reduce the force with various changes.

are you sure you aren't shifting under load , or thereabouts?
Are you hard on things in general?

as you say, it's discouraging that after 5000 kms this has occurred, so clearly if you do not find a specific reason that can reduce the tension, you'll have to keep track of cable life and pre-empt a problem.
I wonder if a silcone spray lube (clean, non sticky, but very slippery) on the bend area could help things long term? I use this stuff in bike and house stuff and am always amazed by how it reduces friction--I use it on my old 9 spd brifters, my old 90s mtb front suspension fork to drastically reduce fork stiction on this very old simple fork , its my canadian winter bike; on sliding windows in the house (amazing how easier they slide after, and for a long time)

Here we have a product , spray can, called Jig-a-Loo, you can look it up and see its specific properties. Im sure there are similar sprays where you are in the States.

good luck, I'm curious to what you can find out