Despite the point in my comment about power cable extensions coverings becoming hard through the lack of plasticizers, I confirm your point about overplasticized PVC in instrument cables.
I have a lot of instrument leads that I thought were silicone only to find that after a year or so they've gone hard. So much so that new unpacked ones can no longer be easily straightened (the kinks remain unless one heats the cable up and then straightens them).
Despite availability issues,the problem is trying to determine what's real silicone and what's not.
I used to buy vulcanized rubber (like SO cable) test leads from Oldaker Manufacturing in Dunkirk, Ohio. They had supplied them to Tripplett when the latter was still manufacturing meters in Bluffton, Ohio.
The ones I've had for decades are still working well; they're reliable and flexible.
I learned about the utility of rubber after becoming frustrated with PVC leads being stiff in cold weather. I stepped into Oldaker's shop on the way home one day and asked the nice older lady there about buying some silicone leads.
"Are you sure you want silicone," she asked. "Most people want rubber."
I was sure that she was nuts and that I knew exactly what I wanted, but I played along. She disappeared and came back a moment later with two sets of test leads: One with silicone insulation, and the other with rubber insulation.
I examined them both. I picked the rubber ones; they somehow seemed both tougher and more flexible. No regrets. I've bought more examples over the years for different things. (Perhaps it'd have been smart to have also bought some silicone leads from them as well, for long-term comparison. Alas.)
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Anyway, Oldaker Manufacturing burned to the ground about 10 years ago. Whatever tooling and supplies remained after Tripplett packed up and left is simply gone.
Which is a bummer for a couple of reasons: First, they seemed like very nice people who were just trying to get by after their heyday was over. It was very much a mom-and-pop facility by the time I came 'round.
Second, I subsequently cannot find any reliable source of rubber-insulated test leads. It's only been a decade so far, and I do look occasionally. They do not appear to exist.
(There's probably be an opportunity here for someone to make test leads using vulcanized rubber and sell them, but it's limited. If it works and becomes popular, then someone overseas will clone it. And when they clone it, then others will follow with their own take. After that, it's just a hop skip and a jump before we reach the end game: Dilution.
Wherein: Overplasticized PVC test leads that are described as being rubber will be easy to find, and actually-rubber leads will be impossible to locate in the sea of noise.)
Despite the point in my comment about power cable extensions coverings becoming hard through the lack of plasticizers, I confirm your point about overplasticized PVC in instrument cables.
I have a lot of instrument leads that I thought were silicone only to find that after a year or so they've gone hard. So much so that new unpacked ones can no longer be easily straightened (the kinks remain unless one heats the cable up and then straightens them).
Despite availability issues,the problem is trying to determine what's real silicone and what's not.