I was recently installing a some Shimano hydraulic brake lines on a bike which uses GRX levers when I noticed brake oil leaking out of a port on the side of the lever.

I did some research and found out that this is caused by a broken or unseated diaphragm, which can be replaced: the part you need is the STR9120 Lid Unit.

Follow me on Instagram @spinningtruecycling
My Website: www.spinningtrue.com

Thank you for showing your support by liking, subscribing & commenting. If you feel that you gained something from my content and would like to help me make more, consider buying me a coffee here: https://www.buymeacoffee.com/crazycyc...