What is the purpose of sliding pin lubrication on a single-piston floating front brake caliper?

1. To allow the caliper body to slide smoothly, ensuring both the piston-side pad and the opposing pad apply equal pressure to the rotor.
2. To lubricate the brake pads so they do not squeal when contacting the disc.
3. To seal the brake fluid inside the caliper piston bore.
4. To prevent the brake disc from rusting during wet weather riding.