86 951 Driver

Is there anyway to be 100% that a fuel rail is leaking? I imagine if it does crack the cracks would be very small. I noticed today my cam cover had a little wet spot on it. I am not sure if it is fuel or something else. It was right under the side fitting for the jumper line. If it is fuel then it would be either from the Jumper Line(rebuilt stock part) or its the fuel rail that is leaking.