mirage mask and old gel

hi,

i have a resmed mirage mask (old one) that had a gel/silicone cushion that was left in too long. i took the cushion out, but the retaining ridges are gummy. what can i use to clean those out? regular isopropyl alcohol isn't doing it. i'd assume denatured alcohol would, but i don't want to try it, before knowing it won't ruin the mask. thanks

Maybe get a new mask?