@daveyf --
For those with other types of driver design, what are your concerns about the extended usage of this kind of driver as it ages?
I’m not concerned, really, but I’m invested in this subject nonetheless. My speakers are all-horn loaded using compression drivers for the midrange and tweeter, and a (hidden) 15" bass driver with treated accordion cloth surround in a folded horn. None of these drivers are directly visible (only the exit area of the compression drivers via fine-masked grilles), and so their diaphragms and surrounds aren’t exposed to light - not even the bass driver, which is situated behind a some 3x13" slot (its exit area into the folded horn). Treated cloth surrounds at the end of paper cones, even when exposed to light, usually last decades, and the Mylar and paper composite material of the tweeter and midrange drivers respectively should have close to indefinite lifespan. All things considered (including cross-over components, cabinetry, etc.) I would expect my speakers to perform immaculately (way) past 30 years, quite comfortably.
If anything it seems to me regular use of one’s speakers is the best way to actually preserve them, and in your specific case I wouldn’t worry about the rubber surround of the of bass/midrange driver. Try to avoid them being exposed to direct sunlight, and with rather normal atmospheric conditions, humidity and no severe temperature variations (other than what normally occurs when opening windows and such), I gather you should have decades of trouble-free service from your beautifully crafted, well-engineered and high-quality speakers.
