Water leak under window

Hi all,

Just to preface - I did search the website for threads describing window leaks before I posted this thread - however, I'm not sure I found anything specifically describing what I see, so I'm going to post my situation and see what you folk think...

Last night we had a high winds and heavy rain (weather service had warnings issued, etc.) -- I went out this morning to check the TM, and found that one window in particular had water beneath one window (small amount, not enough to soak anything in any significant fashion).

Strange thing about it - the water appears to have come out of two of the screws securing the lower curtain track. If I had to guess, I would guess either a) some portion of the window seal is bad, or b) the window's drainage mechanism became overwhelmed, allowing water into the wall, which partially or entirely escaped via the curtain track screws.

The TM is frame-level (not fridge-level) front-to-back, although it's not exactly level side-to-side (not far off though).

One other silly question - is there any easy way to tell if a shell is retaining water? I read one horror story from several years ago, and I want to make sure I don't encounter that kind of grief (we bought this unit used, and thus have no warranty to fall back on).

Anyways, any advice would be greatly appreciated!

Thanks,
John