This brake system is designed to automatically adjust the clearance between the disc brake rotor and the brake pads by the piston gradually protruding according to
the wear of the brake pads; therefore, when you replace the brake pads, you need to push back the piston.
If oil adheres to the brake pads, if the brake pads are worn down to a thickness of 0.5mm, or if the brake pad presser springs are interfering with the disc brake rotor,
replace the brake pads.
The illustration uses BR-M7000 as an example to explain.