Further to the idea of dried out sidewall refurbishment. I picked up a nice set of green Wildgrippers today, front sidewalls are mint, rear sidwalls were very dried out, sorry, didn't take a before photo but trust me, they were pretty dry, not as bad as the Mega bites above though.
I did my best to clean up the green rubber and not having any dubbin to moisten the dried up side walls, decided to try proofide instead (Brooks saddle cream for those unfamiliar). I think it worked like a charm, time will tell I guess.
Pictures of the bike they went on and close ups:
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