I had that problem too with the right Shimano 105 8-speed Brifter (shifting/braking levers).
My solution? I unmounted the lever, just enough to have acess to all parts, and cleaned it with a small brush, WD40 and compressed air. Then, make it work up and down several times, so it releases the dirt/ old grease.
I had that problem too with the right Shimano 105 8-speed Brifter (shifting/braking levers).
My solution? I unmounted the lever, just enough to have acess to all parts, and cleaned it with a small brush, WD40 and compressed air. Then, make it work up and down several times, so it releases the dirt/ old grease.
Lube it, and mount it again.