You know what, that is funny. I have had mine flushed about every 15-20,000 miles and it always seems like the crew working on it has a leak or something where they have to start the flush over after reseating the hoses. Makes a little more sense now that I know the top is the return which is counterintuitive.
Just so I read clearly, 5/16th is the fitting size. After reading the write-up, thinking about a tranny cooler as well. I love this site!!!