ok - when cold the off rear brake makes a grinding sound (but only for a few minutes a day) so today I had the drum off to have a look fully expecting to replace the shoes, the trailing shoe was worn more than the leading shoe and both shoes had a glazed look (I was expecting to find the friction material riveted to the shoe - and the rivets grinding on the drum - its been a while - 30 years since I changed brake shoes) .The near side shoes show the same uneven wear but not the glazed look, and doesnt grind.
Picture of offside rear drum here
Whats the minimum thickness before they need changing?
There is no obvious leakage of hydraulic fliuid but could a little ooze out, cause the grinding and leave the shoe glazed?