Discussion about the Korg PolySix synthesizer

i have cleaned the key contacts on my polysix  probably 4 or 5  times even using diffrent solvents at times. I always get everything back and everything is fine , then after some storage  time  some keys stop again ...i can get them back by  fast repeated pressing and then they work fine for the playing session, but some of the contacts loose it over storage again. I wonder id the problem is NOT in the cleaning , but something else. How can they get so dirty so fast? Can they oxidize overnight?  or is the problem one of alignment of the disks or the stiffenning of the rubber  contact holder?  this is frustrating and just doecnt make sense as a cleaning issue.. the principle is very basic, 2 conductive pieces touch ---and they DO WORK, just sluggish to respond.