Hi all,
I read a thread on CN the other day about a similar question & nobody came up with a good solution.
So I thought I'd post my google research here as I'm not a member there.
Anyways the best thing that I found to use on rubber is actually talcum powder.
It's actually used in the manufacturing process to keep rubber soft and supple, to absorb moisture from oil/grease and to cut down on friction. (contains silicone element)
Also maintains the elasticity of rubber and will not dry out or damage it in any way.
So I gave it a go on my TMB 40mm paragon eye cup and grips.
All done and dusted.
Hope this helps. Only time will tell!