For me, it would depend upon a few factors. First, what is the difference in down-time? If the truck will be down for the same time whether you fix what's broke or rebuild the whole thing, then spend the money (if you have it) and rebuild the whole thing. However, if parts are on back-order or if it just takes a while to rebuild each hole, and if I couldn't afford to have the truck out-of-service for any longer than necessary (customers are depending upon me and this truck, etc...), then I'd just fix what needs fixing and worry about the others if/when they present themselves to be a problem. Second, which I've already alluded to, what does your budget allow? If money is tight, fix what's broke and worry about the rest if/when they give you problems. If you have the money, go ahead and rebuild the whole thing. Third, is this a hobby truck or does it need to be 100% reliable? If it is just a hobby truck, I would fix what needs fixing and leave the rest alone. I can mess with the others if/when they present a problem. However, if I need to run the truck to earn a living, then I'd spend the money (if I had it) to completely rebuild. Thing is, those "good" holes might last another 20 years...or they could fail tomorrow. Same with the new parts. Only difference is that the new parts and the labor rebuilding 'em will probably have some sort of warranty if they fail tomorrow. All you know is that they are testing OK right now, out of the truck & on the bench....which doesn't necessarily guarantee they work properly while properly installed. Tough call, for sure...