Noice! Read your thread- the simple answer was, "You had a leak" but as you rightly point out, it can be like finding a needle in a haystack! Troubleshooting is a skill that seems to have been LONG forgotten in the age of instant fixes and "it's broken, so just replace it instead of trying to fix it."
Nice work and nice catch. Sometimes all it takes is another pair of eyes or 24 hours of NOT looking at it in order for it to jump right out at ya.