I boiled the bejezus out of those knee pads and all it did was make them hot. I remember installing hard rubber tires on an old riding mower my Dad had in the early 60's. We boiled the tires and they popped right over the rims.Dipping parts like carb boots in boiling water is the easiest way to soften them for installation; they don'tr stay soft, though.
The nitro-methane and alcohol is an interesting concoction. Sounds like RC engine fuel to me. Don't get that near the paint on your bike!!
Years ago, I either read an article or was talking to a tire and rubber expert about tires. I learned that one of the reasons tires harden up if left to sit is the oils in the rubber need to be warmed up for them to keep the rubber supple. I have to be honest, and struggle with understanding that, but I have also seen just how sticky my tires would get when I'd bring my bike in from a series of hot laps at the track. I suspect that road use is somewhere between track temps and gooey rubber and no use and cold, rock hard rubber.
I know UV plays a major role in rubber life. I have an original pair of Firestone sawtooth tread tires that came on my Knuck. They were installed sometime in the 50's as best I can tell. They are hard, but they are otherwise in excellent condition with no cracking, checking or rot of any kind. I know that the bike spent the last 50+ years under a canvas tarp in a garage so there was zero UV attack.
Ozone is another enemy of rubber. I have had rubber boots on electrical parts in my boat crumble after a year or two. They are hidden from any UV attack, but out in the open air all the time. I assume Ozone is the key culprit for that damage.