Thats brake fade, vented disks and decent pads to cure - silicone brake fluid too if you can be bothered and are feeling flush
Here ya go chap... Exact same kit I got.
Just stip the old sliders off, remove any rust with 00-gauge wire wool, regrease with the supplied grease and reassemble.
Use a foot pump to remove the piston. Remove rust as before. Renew seals and reassemble, use brake fluid as lubricant to aid reassembly. Its a good idea once you have the caliper stripped to give it all a damned good degrease, wash and dry. Paint all non-wearing areas and parts with smooth hammerite and allow to dry, I baked mine in the oven at 50deg for 2 hrs. Then proceed with reassembly.
They'll look brand new, as in
this thread where I sold the ones I reconditioned...