As an A&P of nearly a half century of experience, ANY time more than one cylinder needs to come off of the engine, it’s best to remove the engine and send it into a shop qualified to deal with the whole process. The famous – or, now infamous (after a recent EAA webinar) – A&P IA Mike Busch will tell you that all day long. The case halves don’t like being left to hold itself together with more than one cylinder removed. I’d bet BIG money that the tool(s) necessary to hold the case halves torqued together properly was NOT used on your O-235 while it was apart. Next, new cylinders have become relatively inexpensive (if there’s such a term in airplane ownership) so "overhauling a cylinder is a penny wise and dollar foolish transaction … especially when more than one has to get help. It wouldn’t surprise me at all if you don’t next tell me that the crank or cam or something inside isn’t happy or you spin a bearing and the engine had to come off. Engines are haunted … if you haven’t learned that. I like to tell people that the parts of a “happy” engine get married and like to spend time together. You DID allude to this. I recently sold a 51 year old airplane with its original O-320 engine still together and never been apart. The second something like what you described here would have happened, that engine would have been off the airplane for full teardown.
If you took the Lycoming school // forum at Airventure, you’d have heard the Lycoming people tell you the same thing. I don’t know what kind of mechanic wouldn’t notice multiple successive cylinder R&R’s and tell you to keep doing that. Your mechanic is suspect.
Finally, I read and re-read your article and tried to figure out why you’re mentioning a borescope in the title and didn’t say anything further about it ?? What was the borescope used for … a colonoscopy? In recent years, the use of borescopes has become more widespread and the FAA now recommends their use. That said, they are but one tool in the toolbox of a good A&P. Talking to the owner, records search, analysis of where an airplane has been / how it’s been maintained, oil usage and frequency of changes, oil filter or screen, oil cooler or not, temp records (if fitted with a monitor), frequency of use, training or private usage et al are all part of the analysis before taking action. There’s more to this story that you didn’t cover.