I have seen this issue many times on this forum ----- concrete is not level, so one side of the door does not seal properly. The answer is you need to make or buy a angled filler for the bottom of the door. But if this is so common, I figure somebody must make and sell these pieces. After a couple of minutes with Google, I found this:
Its a bottom garage door seal. They don't explain intended use, but the high sides must be so that you can angle it to the door/floor. I would think that a garage door professional would have a solution for such a common problem as the concrete floor not being level. If one company makes a bottom door seal with extra adjustment, you can bet a dozen others do also.
http://www.advancedplastic.com/products-bottomseals.php
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