A forum member suggested silicone brake fluid some time last year. That's what I've been using and it seems to work really well.
I would never put anything on belts, by the way. I just use it for door/hood/trunk seals and every now and then on the rubber part of the wiper blades.
I will concede about using silicone lube to lubricate silicone O rings, because the literature is not clear. However, the SYNCO mfg. brand of silicone grease is listed as non compatible with silicone rubber in the chart linked above.
Or, are you saying that EPDM rubber is not a common vehicle elastomer?