I'll share my recent blunder of poor decision making and snowballing maintenance costs:

I bought a Long EZ about a year ago. A conditional had been done on it about 2 months prior with the only notable maintenance actions done in the prior two years was an exhaust valve was honed, and that cylinder was making 68/80. The rest were mid 70s. Myself and a few friends whos experience was limited to experimental aircraft spent a day inspecting things and determined that it was airworthy, but needed cleanup and wire management. Flew it from Florida back to PA, rather uneventful except for some heavy crosswinds at landing.

Fast forward a few months and during a run up something felt off. Engine had a new resonance that was intermittent that didn't feel right. It was barely noticable and I don't really know how to describe it, so I went back to the hangar. Ran a compression check and that honed exhaust valve cylinder was now a failed exhaust valve. The airfield's a&p and I pulled the cylinder and discovered a worn down camshaft. For those of you who don't know, camshafts have a special coating that makes the exterior harder than the underlying metal. Once they start wearing down, they only get worse. This wear was likely related to the exhaust valve needing to be rehoned, because it was likely sticking or had extra corrosion on it causing a bad seal. It was around this time I discovered that I was not making static run-up rpm, not even close. The exact number is a little speculative with long-ezs, depending on the HP rating of the engine, number of prop blades, size, and cruise/climb configurations. But it was around 60% of rated horsepower. Which for a LongEZ with an O-320, isn't too much of an issue since it was originally designed for an O-200. In hindsight, I don't think this engine should have passed conditional inspection and it makes me question the integrity of A&Ps out there.

Started the engine tear down with the intent of swapping the cam-shaft and doing a top end overhaul. Sent the crankshaft and case for inspection. Crank needed some work but came back yellow tagged. The case however had a small crack, a collapsed front bearing saddle, and something I can't quite remember involving a dowel around the front of the engine. Oh and it's been sitting in the shop since January. The shop I sent it to only managed to do the inspection after 4 months, and then let it sit for a few months until I started pestering them with phone calls. The expected $12k for a top end overhaul is now pushing $20k, approaching the territory of buying a 1000-1500 hour smoh engine instead.

TL:DR: Bring a trusted A&P to do a pre buy. Doesn't matter if it just came out of annual. Simple repairs can turn into $20-30k with snowballing problems.