I was digging through some boxes of spare bike parts in the garage a while back, and came across a pair of fairly nice Diadoras that used to be my (favorite, most comfortable) racing shoes. But, not sure if it was their age, or the heat in the garage over several years, but they had started to come completely apart and had gotten gooey (like wet and oily), with solid chunks coming off.
But another pair of Diadoras, that were a lower-end model, and that date back to the same purchase point (2001 or so), were my regular training shoes, are still in service. One sole had started coming loose years ago, but I used some shoe repair glue, and fixed it right up. Then, last year, while at a water break halfway through a long-ish ride, I realized the other sole was coming loose. I nursed it home without issue, and re-glued that sole, and it's been good-to-go ever since, and they look to have a fair bit of use left in them.