Sorry you're not happy with it (or is that 'no longer happy'?), but unless you know something I don't there're no "plasticizers" in Silicone rubbers, that's something done with stuff like vinyl and other materials that 'dry out'.
I don't claim to be a materials expert but for one, it's very misleading to call silicone a "rubber" as it's technically a plastic, like all resin polymers. Then if you check the "Handbook of Plasticizers Ch11" that is available here:
http://www.sciencemadness.org/talk/files.php?pid=247355&aid=18568 you will see on page 357 (page 85 in PDF) that there is quite a long list of plasticizers commonly used with silicone, including the now banned phtalates and many other horrors.
We're not supposed to discuss materials safety in the vaporizer review threads as per the forum rules, and as I stated before, we SHOULDN'T HAVE TO ALL BECOME MATERIALS EXPERTS when just using vaporizers, but unfortunately it's the feeling I have, especially with all these portables coming from China. We end up having to read about the safety of X or Y and determine if it's good enough for our liking, and I pretty much dislike this aspect.
So plasticizers or not, when a material aspect and texture change over time like I'm seeing here (color change and becoming harder and brittle, losing chunks) it's a clear sign, at least in the case of plastics, that some of the components leached away.
And when you can taste or smell a material, it also means that there are free molecules escaping and becoming airborne and reaching your nostrils and taste buds. I have other vapes with silicone inside and they don't smell. All Ascent users in this thread complained that their device smelled when new, this is a fact. With mine after a while the smell was barely noticeable and it was fine but after having switched to other devices and coming back to it, and with the newly exposed surface (the part where the chunk was) I can clearly smell/taste it again.
Is it safe? I don't know. Safer than combustion? Most probably. But that was not necessarily the point. I just wish they used either a better quality silicone or a completely different material altogether. And I hope they won't use it everywhere in their next device. It might be a placebo effect, but when I use my Zion or my Firewood, which have wood, stainless steel, nichrome and glass as the only materials, it feels much healthier, and both of these devices had STRICTLY NO SMELL when new and didn't develop any over time.