[ossiblue]

From your pictures, it looks like the leak has already been "fixed" once using some kind of patch. The second picture, especially, looks like a rough, unsanded compound has been applied and painted over. From the look, it appears a PO tried the same thing you are considering--fixing the leak without removing the tank. If that's the case, then I think you'd have to remove the tank to do a complete and secure repair. Just draining the tank and sanding the area probably won't be enough as you would need to be sure no oil remains in the patch area and on the metal. If it turns out the tank was previously patched, I'd bite the bullet, pull the tank, remove the old patch and have the tank welded/brazed for a permanent repair.