I looks like this is the cause of the issue scientifically.

". . . . . . .
There is therefore a large range of both sequential (or chain) reactions and competing reactions and that the ones which predominate depend on factors such as the composition of the vulcanizate as well as the influences of heat, light and metal catalysis. In heat ageing we are balancing the rate of reaction of oxygen with the elastomer and the rate of diffusion of the oxygen into the bulk material. If the temperature is relatively low, it has been postulated that for an unprotected vulcanizate diffusion predominates and therefore there is slow oxidation throughout the product, but as the temperature rises, the rate of oxidation increases much more than the rate of diffusion so substantial oxidation occurs on the surface and an oxidized (hard) surface skin is formed. As oxidation continues the chain breakdown may become more significant and the hard surface then softens and turns sticky. To complicate matters further, under certain conditions this order can be reversed and an initially sticky degraded surface can harden with further oxidation.
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The article says, it is possible to reverse this!!! Now the hunt begins, "How do you Re Oxidize Rubber or Plastic?" in DIY manner. If I figure it out, I will update the post.

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