If you fill in cooler temps and/or do not allow a small air space (5-10% for temperature expansion??), and/or do not make sure retracted before filling, you stand a big CHANCE of OVERFLOW on retraction, or large weather temperature increase? (My $0.02, Just a gut feel, based on years of mechanical experience.) I have read MANY say "fill until full", but can see where that may well be a mistake. BRAKE Reservoirs/ BRAKE FLUID, as example, GET HUGE HIGH TEMP Change, maybe even boiling, BUT the reservoir CAP has a built-in EXPANSION SPACE AND RUBBER CAP SEAL ENGINEERED INTO THE CAP DESIGN, and additional compensation in lower fluid as brakes Wear... NEITHER an influence in (MY Dewald slide hydraulics) that I recall