I just had this discussion with Charlie Erb last week. His take: the guns were designed with the thought that, as combat weapons, they would have a short life. The bolt/op rod wear issue is just something that any 60 operator is going to have to put up with. Grab replacements whenever you see them and keep an eye on your own for wear. As for the ones being flogged on Gunbroker, he says "trash". Another dealer I know says most should work or can be made to work. I personally hunt for those without repairs and that means I want to handle and examine the parts before buying, ruling out internet sale sites for me.
If you want good ones, US Ordnance / Desert Ordnance sells new-manufactured stuff that's made better than the old mil-spec stuff, but you'll pay for it.