Did you notice any fuel in the trunk itself?

Did you remove the bolt-in panel separating the fuel tank from the rest of the trunk? That's the only way to be sure you see what's going on.

There should be several possible points of leaks - There's an overflow hose for when you're filling the tank and it you overfill it. That drains from the fuel filler opening through a hose (I think) in the trunk and out the bottom. Those can get clogged over time. You may be lucky and there might not be any diesel in the trunk itself. I still think you need to remove the panel to see that hose.

There's a grommet between the tank and the fuel filler opening. If you overflowed when filling, and the grommet was bad, fuel could have gotten in the trunk. Though I doubt it would be enough to cause what you're seeing.

The tank itself could be leaking from some point. Once again, you'd need to remove that panel to see where.