do those things ever wear to the point they have to be replaced?
do the dealers sell them each?

 

Yeah they do go bad I had one of my front ones that was completely frozen and rusted out.

Autozone sells them for like 12-14 dollars for each caliper and it includes everythign cept for the grease and the rubber boot.

 

I had them rust in my 240sx. I had to heat them up get them to pop out. They were rusted in bad. I had to run them over a wire wheel to sand them down to a smooth surface them lubed them up and replaced them with new rubber boots. Nick