Update: Had the original window installer in today. we took a hose and sprayed all around, in, above the window etc; all weep holes drained well, condition could not be duplicated. Hosed water on roof above the area and around roof solatube in case flashing wasn't good. Roof does have good drip edge. It's conceivable that a gutter that empties onto the roof could be a culprit but after thorough hosing no visible water in attic. This was all based on a corner of peeling paint under the window sill that seemed to swell during a heavy rainstorm. Could be a bad paint job that trapped humidity underneath--there may not have been a leak after all. We will be replacing a through the wall ac/heating unit underneath, so when we open that up we should know more. The installer said if this kind of leak was going on for ten years that sheetrock would be much more powdery, brown and you could put your finger through it. This is also next to a stove where cooking goes on. So things may not be what they seemed, but I think we've narrowed down the issues today. Thanks for all the great suggestions.