Copper coat is petroleum based and it reacts to rubber causing it to swell in time and semi seize or not able to retract back
It needs high temp silicon based grease
Can't tell you where to get it in china etc
Brembo has it
I use it in NZ for brake pins as the factory should as well
As for changing pads it's little complex but unbolt the caliper
Remove the cradle clean slides
Fit the cradle back and fit pads
Yeah little hard to explain a it's fiddle on a bike and each caliper little different