I've had the laser blocks go bad several times. My first sony was back in high school, for me... maybe '90? It lasted a good while, but eventually stopped tracking the discs. Everything else worked fine. My dad has had two NADs go tits-up on him. Some random tech guy said lasers have a rough lifespan of 10 yrs, depending on usage. My experience is probably more like 7 years with moderately heavy usage.
Never seen a belt inside a disc player... plastic gears for the drawers in the ones I've been inside.