It's a bit of a messy operation, but you need to clean the inside of those couplers.
There is a ball in the center of the couplings that is spring loaded - holds the ball outward to seat and seal.
More than likely there is a little dirt where the ball seats - had this happen a time or two before myself.
First, take a clean rag and clean the inside of the coupler the best you can. Then put the rag on the end of a large screwdriver and push in on the balls a couple times. When you do this you will leak some more fluid but it won't be under pressure. Clean the coupler again with the rag.
Sometimes I had to do this procedure a couple times before it stopped leaking. All it takes is a small amount of dirt/grit to get between the ball and the seat.
