My rear light is full of humidity after very hard rain. I don't know how it entered the light but it's there for 3 days and it can't get out. Is there any weakness in the sealing of the light? something I can repair?

There must be at lest 1,000 posts about this topic posted on this board. Just stick some goldfish in there. I have tadpoles in mine, but I like being different.

if u r under warranty Mazda will replace , wifes car had both replaced

Its the dirt build up on the Rear light Gasket that causes these.

But yes, its been discussed like 100000000000000000000000000 times so SEARCH is your friend.