Xantia rear brake calliper

[Hell Razor5543]

If the grease at that point got hot, I wonder how hot the discs and pads would be?

[Old-Guy]

Having done this job (de-corrode the rear callipers) on the Green Lady last September and having an understanding of galvanic corrosion:

Over the course of the week before, I soaked all the fasteners (don't forget the nasty little 5.5mm-head disc-retaining screw) and the gland nuts several times with 3-in-1 Penetrating Fluid (perhaps not quite as good as PlusGas, but all I could get).
Despite (or perhaps because) expecting, and being prepared for, the worst, everything came undone without any dramas.
Having thoroughly cleaned off all the corrosion, I spray-painted both the calliper and the arm faces with one thin coat of high temperature paint (black for wood-burning stoves) and made a thin gasket to go between. The new (Citroen) bolts came with a thin coat of preservative so I left well alone. I very definitely would NOT use copper grease as the introduction of yet another, even more 'noble' (more electropositive), metal can only make the corrosion problem worse.