Hey Steve,
As you have already figured out it is a quick disconnect for the fuel line. No doubt the previous owner got tired of the fact that you can't fully lift the fuel tank because of the short fuel line that goes from the tank to the throttle bodies. Not sure why it is leaking but it could be that it isn't rated for the pressure involved with a fuel injection system. Off the top of my head I can't recall the pressure in that line but it should/might be in the manual and a call to Motion Pro could confirm what that fitting is rated for. In the meantime, definitely be a good idea to replace it with a stock non-leaking line.