69Hemibeep is correct, It is the 5/16 sending unit and yes it does not have the return. As for gas stains it is hard to determine where exactly it is coming from as the fuel travels the lip of the tank. At first I thought it was the lock ring but I have installed the oem one the sender. After that I scoped the vents on the inside of the tank and they are oriented correctly, and the lines are hooked up as they should be. Confusing indeed..... It does indeed vent vapors and stink the garage up after the initial little bit of barfing up fuel...

For the other posters, it has 1/4 tank of fuel in it.

I will try and blow through the vent lines.