These are the bushings that the caliper slides on. These rubber boots are the gripping surface that affects pad contact with the rotor and release. Their rotors and pads change, as do those rubber parts. Go crazy and make caliper seals and boots! I assume it will be a floating caliper fitted with one hydraulic piston per caliper. Is the fuel consumption bad? Presumably the calipers are sticking to the pins and caliper bracket.