Radnor I don't know if it would involve a lot of work in the code or not, but if it's not too much work, perhaps you could make it so that when you get a bot in the dump, the higher rank the part is, the higher chance it would be not working. Because right now, there's very often only one defective part. For a lower tier bot, it's not an issue, as the parts aren't that great. But with the introduction of higher tier bots, who could be full of A or S-rank parts, it could become an issue, I think.
By making the higher rank parts of those bots more often not-repairable (if the bot is found in the dump), you would prevent a player from getting a full S-rank bot with S-rank parts (and only one part not functional), and it would then become a real quest to repair an S-bot rank bot you found, first switching the many not functional parts with crappy D-C rank parts, and then slowly upgrading them back to A-S rank when you get lucky and find one of those parts.
As a in-universe explanation, you could imagine that many people scavenge as well, and the A or S-rank parts that are still working would often have been scavenged by others before you, leaving more often than not only the not-repairable parts.