You can add extra steel, if discs seem to be OK but too thin by specs. Check manual for specs and measurements of discs. I bought ZX11 with worn out aluminum pressure plate and brand new discs. Clutch was slipping 100%. I installed extra used steel disc, solved!!!Just reread noticed you said “disks are fine”. I would assume if friction plates were completely worn out, it would slip no matter how many pressure plates u added.