What model? Poly 6? POly 8? Poly800? Poly 61?
Are these the strips of gray rubber contacts with a little round volcano for each key, and under that volcano is a black conductive dot that contacts a pc board? They are in groups of maybe 6 per, and are held to the board byt a few littel rubber points that stick through holes in the board?
That is earlier ones. Later ones added a black rubber ring under there around the center one, making it a double contact.
And later still there were two rows of domes down the strip or long double domes at each key, meaning two rows of parallel contatcs on the board.
If so, those pop out if you pull gently up. Note how they go in. The oldest ones are not directional, though there is one on teh end with an extra bump... or something.
The double row ones have a deep one and a shallow one - look close - and it matters which one is towards front.
Clear them all off the board, Qtip and isopropyl, wipe down the board contacts.
I also use Qtip and isopropyl lately on the rubber contact. DOn;t use contact cleaner. I scrub each little dot with the Qtip. I don't use solvents on the rubber. I used to use pure freon, but that is a thing of the past. Other cleaners are solvents, and don;t use them.
SOme contact strips may still be available from Korg. I think most of those were Fatar keybeds, so sometimes strips from other brands that also used Fatar beds will wrok.