[Alan Brinton]

I wouldn’t trust me on this one, but the first thing that comes to mind is a silicone treatment of some kind. I think once the rubber starts to crumble it’s too late, but silicone is supposed to soften and help preserve rubber by replacing the “plasticizers.” I have the first of these two products that I applied to gaskets on a couple of melodicas, but I think Melodica-Me subsequently advised against this. I haven’t seen ill effects of it, but it didn’t noticeably improve the gaskets.