When to replace the rear brake pads in a Audi A3?

My 97 A3 - has done 84000Ks - replaced rear pads with approx 1.5mm of depth left on each pad. Would recommend use of tool to screw slave cylinders back in to shoes prior to fitting pads - slaves have to be screwed in. At same time, wipe brake bleed nipple clean, place plastic hose over brake bleed nipple and sit other end in clean small jar - unip nipple as you screw slave in to allow excess brake fluid to escape slowly. Refit new pads.

I live some 400k from dealers and brake repairers - for issues of safety would recommend a brake specialist - cost a set of pads and 1 to 2 hours labour.