Ok, I've figured out how to add images.
Here what I've found:
All fasteners got out of their places, looks like wrong type was used. It looked to me fasteners used were too thin. Oncoming wind pressure plus vibrations plus improperly spread sealant and I've got this nice picture.
I am not sure still whether it is Thor design flaw or assembly guys curved arms. Or both.
I was damnably reluctant to dо it at our dealer (it is Davis, CA, La Mesa RV branch, the worst service in USA I ever met). Fortunately in law - a really handyman - came to stay with us for couple months. He encouraged me to fix it it ourselves.
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