Leaking gas filler tube on 35

[Coupe35]

I installed a new lead washer on my 35 gas filler tube but it still leaks. Is there a good sealant that I can put on the lead washer to keep it from leaking? I cleaned all the threads real good so I know it’s not because of that and got good leverage on the wrench for a tight fit, I know somebody suggested using O ring but I would rather stick with the lead washer. Any ideas.