I have 400 8-tracks of which over 130 / 140 orso were nos sealed or recent limited anual production batches brand new even (mostly blanc tapes) The rest all used pre recorded tapes of which twenty or so nos or brand new pre recorded tapes.
Good rubber does not desintegrate under well stored normal frequent use in house or in car conditions or outside if portable player is used. And my rubber tires including very extensively over 50 years old used 8-track cardridges of mine are all still 100% like new inside including tape and rollers.
Unlike the pinch rollers, tires and belts in cassette decks from certain consumer electronics manufacturers, mosty Matsushita, and from Philips group have indeed used bad cheap rubber that didn't deserve the name galvanized rubber, and that's a different story than with 8-tracks and R2R's and TT's which tires and belts in most cases are still like new, unless very extensively used thus fysical wear or otherwise abused / badly stored)
However notoriously 8-track cardridge rollers are from mostly one or two always the same cardridge brand over here in the America's being from the GRT (an UK based brand manufacturer part of the Philips group back then) Almost always crumbled disformed, bonded even with the tape in the cardridge and of an odd unreplacable roller size. Although one can retrofit these roller rimm's with the right size rubber gas etc hose. Most of these cardridges have be trown away or the tape transfered, moved to another cardridge decades ago. The other would be of the first 12 years or so of the Learjet tape production. They used a rubber that did not crumple, but turned into goo with often the tape bonding with the roller even. Mostly Ford Lincoln Mercury automotive and most aviation and cardridges for marine use, including there demo tapes, have that problem. But unlike GRT carridges, these rollers are of a standard bigger size including the center hole for the shaft so another rubber roller or plastic roller can be easily installed. (But most Ford Lincoln Mercury cardridges, which thus often are Learjet type with the goo sticky rollers, are therefore also partly glued together. And that can be another complication ).
So bad disformed goo-ed up or crumpled or hardened rollers in my 8-track cardridges.? Not so much! Only a hand full thus! Bad rubber is the exeption to the rule over here! Even most of my 8 track players and recorders cassette decks and TT's still have there original belts in good condition.
Above are thus two of my 6 GRT tapes which yesterday had the tape transfered by me to the underneath cardridges which had damaged tape inside that was removed and thrown away. I only have to colour scan and print the original labels, and stick it on the cardridges below, to where the original physical GRT tape with it's origional recorded media content is transfered to!