Hot wheel? that's nothing. One day I stopped for petrol and found the back wheel had smoke pouring off it.

Took the wheel off and found that one piston was seized and the pads were down to the metal. Not only was it seized, but I found that one half of the caliper had been broken in the past and had been welded back together by a previous owner. Now why would anyone do that when a replacement caliper costs $75?

As for piston damage, the exposed areas get pretty cruddy and corrosion builds up if you don't check and clean them before you push the pistons back in to accommodate new pads. Once the piston surface starts to pit, it tears up the seals and fluid leaks past them. If your mechanic is replacing the seals and the piston surface is pitted, they'll probably start leaking again.

You can, if you're patient, remove the pistons, thoroughly clean and degrease the piston surface, fill the pits with epoxy and smooth with fine emery paper. but hey, these are your brakes we're talking about. if they are in poor condition, get them replaced. it could save your life one day.

__________________
1987 300e manual 250,000 km (sold)