All foregoing is now digression.
End-snipping and then grinding off the tinplate tangs before desoldering the active pins is the way to deal with these , without colateral damage. Getting inside, the non-resistive tracks are only 1mm wide and one pair of single wiper "wires" must have been right on the edge of one such track so intermittant contact, 1/2mm transverse bend and repaired. Will resolder the remnant tinplate tangs for earthing and add hot-melt around the housing where there is spaces. All 9 of these sliders are the same, but no problem with a channel one going U/S unless someone uses all channels, problem was of course, Murphy's law, on the critical one..
Only info on the side is rather self evident 10KDx2.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on