Diagnose brake issue
I have a cyclocross bike with Ultegra 11 speed di2. Used by a professional so probably it has taken a few hits.
I have an issue with the rear brake, where it gets soft and only works after I pump the lever a few times.
We have bled it a bunch of times, which improved the issue for a while, and replaced the whole hose, which made it better... Also for a while only.
There is no trace of oil on the rear caliper or around the lever - my mechanic and I are out of ideas other than connecting a different lever and see if the issue happens again, but a new lever is quite an expensive buy if I'm not even sure it solves the problem.
Is there anything I can do to at least understand where the issue is?
Most recently, the issue got considerably worse after I fell on my left side in a race.