Start off by cleaning the calipers with brake cleaner, remove caliper, de-rust and remove all brake dust from caliper and pads, clean the sliding pins (the ones you remove with the allen key) and sliding sockets (where the pins fit into). Then apply some high temperature silicone grease (NOT normal wheel bearing or CV joint grease) inside the sliding sockets. Apply some quality high temperature anti-seize paste to the face of the piston, the 'hammer head' ends of the pads, and inside the U shaped section of the caliper opposite the piston. Reassemble, and give it a try.
Oh, who fitted the disc/pads 6k ago?
HTH