the linings had cracked and fallen off the shoes so they had to be replaced, as you said a regular 'drag' polish should make them last longer At work
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"I can't always believe facts I read on the web" - Charles Dickens

winner by default of the tractor vs caravan race

Yer CG, what tends to happen is rust builds up inside the drums and with out proper clinning especialy after a few wading trips to add to matters.
After lots of braking the dums will be hot so when the handbrake is applied and things cool down natural expansion and contraction the linnings tend to stick. when you nect pull away it can literaly tear the linnings from the shoe.