i am not 100% but i think that the a is the windshield post. any way doesnt matter i dont think. look at the corners of the sunroof gutter. you should be able to find the opening to the downspout. this is the most probably location of your mineature beaver dam. when you find it just clean it out.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.