CSX 4000 Fuel Cell (Leaking)

[frankym]

Hello CC Community,

Looking for some advice here with a CSX cobra fuel tank leak. the leak is coming from the large oval plate that is secured with 12 bolts and allows for the pickup tube to pass through the plate and deliver fuel to the fuel pump. I have drained the tank 5 times and replace the gasket with 5 different types of gasket material

Nutrile Rubber 1/16
Nutrile and Cork 1/16 and 1/8
Permatex fuel resistant motoseal
Fiber 1/16

Everytime it leaks like 1 drop every hour. It's livable but I think the reason it's leaking is that there is not a clean flat surface that the oval plate mounts to. First question is do I have an aluminium tank or a stainless steel tank. I know if I remove the tank, the weight of the dry tank will be a good tell but once I know the material, I'm going to order a 1/4 inch aluminum or stainless plate, cut out an oval ring and pre drill to line up with the holes in the plate. Then weld the 1/4 ring onto the open hole in the tank ( I know to dry out the tank and rinse with water to remove all chance of vapor), but this way I would have a solid flat mounting surface to mount the gasket and plate back on the tank. It's a very sloppy opening in the tank and the upper section of the tank / oval hole has the tank folded edge overlay in the design so it's just not a great mating surface. Curious about he material (aluminum of SS) and has anyone else done this?