I have hunted with 870's for more than 45 yrs., still haven't had, one wear out yet. I have a Wingmaster that is over 35 yrs. old, my Son has one that is more than a decade older than that, both shoot as sweet and slick as can be.
I also have one of their older budget models from the mid 80's, it's not even branded as an 870, I think it has Special 12 or something like that on the receiver, but it's an 870. That one is still shooting well, I've killed a couple dozen turkey and countless upland game birds with it.
I also have several other variations of 870's, mostly newer, but all shoot very well, and probably will for another generation or two I suspect.
OTOH, I've had a couple 500's that developed problems within the first year or two of general hunting use. I don't think the 500 is as hardy a shot gun as an 870.
GS