Super custom 3.0 T.D. Fuel Pump leaking

Hello !
Could someone give me some directions about it ?
Yesterday I went out from my Basement and I saw something was leaking.
I don't know what to do, hope you guys can help me.
Is that a serious problem?
Thank you so much

Ah yes - 30 - 32mm bolt, I had the same.

To fix it I loosened the bolt, wrapped masses of thin plumbers PTFE around (just underneath) it and re-tightened it.
Careful - it's the engine (pump) speed pickup terminals, when the nut is loose keep it pulled upwards - I used a crocodile clip + rubber band to keep it from dropping down.

Note, underneath is the fuel pump reservoir that must be kept scrupulously clean! (i.e. the leak is just an inconvenience, the flow back to the tank goes from there).

That's a relatively common leak. It's a symptom of the age of the pump. That leak is an O-Ring that should be replaced. The trick with undoing that nut is to ensure the electrical connector part DOES NOT TURN or the connections inside will twist and break! Just use 2 spanners - one for the nut and one for the connector at the base. I forget the size for the connector (12mm?). Open it up and you'll see the o-ring. I think I used one from a nitrile o-ring kit but I could be wrong. Maybe got one from Toyota.

The ideal scenario is to completely overhaul and replace all the pump internal seals but the local reconditioners charge a stupid sum. I did this seal 7+ years ago and the pump is still going fine.

Thank you so much guys !
I fixed it yesterday and now is not leaking anymore!
You are amazing!