Technical Diesel on top of fuel tank connection

[nwsxp50]

Hi. All.
My fuel gauge stopped working, its happened before ,long story. So I took the cover off between the front seats to reseat the multi plug)normal fix) but found it covered in diesel. I had brimmed the tank a few days ago buy even so. Any ideas where the fuel came from? Is this usual?

 

[Anthony489]

Hi

It is not usual.

I am pretty certain the fuel will have come past the circular gasket that seals the pump/sender assembly into the top of the tank. If you brimmed the tank, this will have been submerged in fuel, but it still should not leak.

See attached pic. I don't imagine the gasket is expensive, you are supposed to change it whenever the pump/sender is removed.