Regarding good components not working when installed on PCB. Have you taken a close look at all the solder joints of those through-hole components on the PCB? Vibration can play havoc on solder joints that were marginal to begin with. I recently had a card reader in my PC that was acting flakey after a couple of years. I removed it and using a loupe I was able to spot a bad solder connection on a connector that looked good to naked eye but was intermittent. I re-soldered it and no more problem!