Howdy,Countrymodeler, Some folks here recommend Armor-all, the automotive interior stuff. SIG may still sell bottles of rubber lube. You might could try googling the glycerine soap mixture. I use SIG lube, it's an old bottle but, still does the job.
I've used green soap and glycerin (messy), STP Silicone spray (OK, lubes while dry.), Armor All original protectant (OK, protects the rubber in LA smog.), and personal lubricant ($1 a tube at the dollar store. Don't laugh, not as messy as green soap and it works.) on rubber motors in the last eight years. I am using the Armor All for most of my flying lately since it seems to be the longest lasting.