There is a hose barb the fuel supply line connects to around 3/4 up the fuel tank. It is sealed by a rubber grommet the barb pushes thru. That could be failing and be leaking. There is also the tank vent at the top of the tank that has a vent hose that runs up the steering shaft.
Like I said above, you are going to have to pull the airbox and start looking around for signs of a leak, even lift up the rear bumper and get the fuel sloshing around in the tank.
All that rubber hose and seals in the system are very old now and were never intended for ethanol fuels, so likely dry rotted and failing. I had to rebuild the entire fuel system in my 2000 xc700 a few years ago, surprised yours lasted this long. The intank pickup hose is known to crack and fall off so you should think about just replacing it all.