Brakes on Bonnie weren't freeing orf very well. Stripped and cleaned them, minor gunge cleaned off pistons, and slider pins. Tin of brake grease £15, enough to keep a busy garage going for a year, stuff that. Copperslip to hand, so I put a thin smear round the outer edge of the piston, job jobbed. Now someone tells me c/slip damages rubber. Does anyone know if this is so?