Chamlux, leaking fluid may not get to the level of seeing fluid levels drop or seeing evidence of liquid on the ‘wheel side’ of the brake caliper. Seeing brake fluid around the dust boot of the piston and finding brake fluid underneath the dust boot IS evidence of a leak that can only be detected with the brakes apart. The piston side is typically on the inboard side of the rotor. Also, cracked and damaged dust boots are only visible with the calipers apart. A sticking piston may sometimes be reset, most of the time not, though, but will not provide even braking force from side to side, causing a pull to the non-sticking piston side. This would be noticeable if the piston requires considerable more force to reset than the other side.