The way to settle the corrosive effects of engine running and atmospheric moisture is for a scientific experiment say by a university engineering department. How about as a subject for a doctoral thesis. Am I the only one that gets tired of eternal unproven blah, blah?
Do we need to have a university engineering student do a research project on running an engine out of oil before we can be sure that the engine actually seizes up?
It's experience that tells us so much. My experience in repeatedly finding water in the engine right after I ran it up for inspection is enough for me. The inspection would find low compression or metal in the filter, and a cylinder would need to come off. Water in the rocker box, water between the piston and cylinder. Even without that, the milky chocolate stuff on a dipstick after a short flight in cold weather proves that moisture, lots of it, gets into a crankcase and mixes with the oil. The terrific amount of water/oil emulsion dripping out of a breather is another proof.
People who have never seen it are skeptical. I get that. But I feel sorry for those that continue to ground-run their engines, thinking they're helping the engine last longer. I have run into too many of those in the shop, pitted cylinders and poor compression, rusty gears in the accessory case, and when I ask them if they've been ground-running it, it's always "yes." Those engines that sit undisturbed don't suffer anywhere near like that.
Burning a gallon of gasoline produces a gallon and a half of water. Most goes out the exhaust, but in cold aircraft engines, some gets past the rings. It's not a doctoral-thesis thing. It's common knowledge for mechanics.