Aux tank cover

[Burt]

When I put more than 12 gallons of fuel in my right aux tank it leaks. I have removed all the screws in the aux tank cover but still cannot remove the cover. This is a 1966 A model 337. There is a boom fairing that covers the outboard rear corner of the cover. The fairing is riveted in place so is not easy to remove. I am wondering if there is another screw under the fairing holding the rear outboard corner of the cover? Anyone have experience with this issue?

Burt