rebuilding the calipers. there are rebuild kits which have new seals. i'll be going through this process soon (already started it).
remove the old pads, guide pins/bushings and carriers. then you need to pop the old pistons out with compressed air (be careful when you do this as when the piston does finally pop, it shoots out - you'll need to put a piece of wood on the other side so as not to damage the piston too). also make sure to wear eye protection when you do that, you don't want any brake fluid getting in your eyes. then you need to inspect the piston and the bore for any signs of scoring, etc. if the piston is damaged, you can't get a replacement and need to get another caliper
clean everything up, if you want to sandblast the outside and/or paint it, now is the time to do that. i dropped mine off to be powdercoated (completely disassembled, they'll dip 'em, tape 'em off and powdercoat them with carriers for $200) and am still waiting for them to finish up. after that, you need to put in the new seals, get the piston back in the bore with the new seals, put in the new bushing kit you got (i went with bavauto's brass caliper bushing kits rather than the rubber), carriers and carrier guide bolts, new pads, bleeder (new recommended, old if you have to - i went with speed bleeders, we'll see how those work) and then you're basically ready to install. you may want to fill it up with new fluid before you put the bleeder in and tighten it just to speed the bleeding process up a bit.
now because my car has over 200k and i'm an anal retentive freak, i ordered all new hoses, mounting bolts, brackets, etc ... if it was on the diagram and was available, i pretty much got a new one
some good links covering this topic:
http://www.unofficialbmw.com/e36/bra..._brake_it.html http://www.bmw-m.net/TechProc/caliper.htm http://www.bimmerfest.com/forums/arc...p/t-31491.html