I took off the right fuel tank, pulled the inspection plate and found the leak problem. The front bracket's rivets where all not driven correctly... Just sheered a little, so the bracket was loose and mostly held in by a little rivet sheer and some tank sealer acting like glue (it's pretty strong). Butt here's no doubt that's what caused the leak. I also made a new re-enforced backing plate. I also added a fuel return fitting so the regulator return lines will go through my new dual fuel selector that will also direct the return lines to the tank they came from. I also plan to add two fuel filters, one per fuel tank. For logistic reasons, I have to swap the fuel from the left to the right tank (have about 18g in the plane and jerry can). So I can't work on both tanks at the same time. The left tank's drain as come lose from its fitting inside the tank, so it will also need to be taken apart, I can also inspect the front tank bracket while it's out...