What's up with this rubber sleeve thing on my brake caliper slide pin (the left one)? That one was REALLY stuck while the one without it was pretty smooth. : r/MechanicAdvice
What is brake grease used for? - Quora
Delphi does not recommend the use of Copper Grease | Auto Torque Magazine
B5225 These components protect brake caliper slider pins from dust while also keeping the lubricant inside the apperture. You must not use copper grease on rubber components as they attack EPDM rubber