I've had the same issue with iso boots, fork scraper sleeves and replica John Bull cable ties - all fell apart within months of fitting.
They came from a couple of sources, but probably all from the same ultimate source.
Some aftermarket stuff is OK, but this stuff was just junk. One fork sleeve actually flipped over on itself and jammed the forks, whereas the last ones at least had the decency to just fall apart and drop off by themselves!
Andover Norton rubber parts every time from now on.