Aidan;

When you write of a caliper overhaul, I presume you mean dissasembly and new seals (and pistons if they are rusted/pitted). Using the big advantage of the cars' hydraulics to push out pistons works well...remove from discs, but not plumbing and use wooden blocks and channellocks to allow them to come out one at a time as a helper pushes the pedal...and remember: As soon as one pops out all the way, fat chance making enough pressure in the system to push out the other caliper's pistons...push them out only far enough so that you can grab and work them out the rest of the way with a leather covered channel lock jaw.

It's not really necessary to split them apart...stainless pistons and rebuild kits are available...DOT5 time?

Brake shoe lining failure is uncommon...fluid from a leaking rear cylinder can definately cause it, but you state there was no contamination...definately replace the shoe...it was probably a one-time thing. I compare lining thickness to a new shoe and replace them as the spirit and judgement move me.

See all my brake service notes at: http://www.intelab.com/swem/service%20notes.htm#Braking%20System

Underseal/undercoating comes of better (yet messyer) with a heatgun. Use extra caution, and don't overdo it around rubber or flammable areas.

Cheers