Originally Posted by
cxwrench
Shimano mineral oil gets very very dirty from pistons, bores, and o-rings. If you ride a bunch you should do a full bleed at least once a year. It obviously doesn't absorb water like DOT but it needs to be replaced once a year if not more.
Short hijack, on.
How do you do it in a shop environment for Shimano? At home I just push new fluid in from the “bottom” (calipers) and collect the old in the cup on the levers, discard that, and continue on my way. It has never failed me. Though recently a guy I know suggested I should drain the system, then reinstall the fluid.