the simplest answer is gold is going to vanish if they found it.
there was an issue some years back - the fed would not allow germany to visually inspect the gold it supposedly had had in the fed vaults for decades, nor allow it to withdraw it.
simple answer? it had long since been sold.
If it was only a case of the Germans wanting to see the gold, would have been a simple matter to simply improvise something looking like a stack of gold bars.
Escort them into the vault, let them even handle the gold bars, etc. - and then, when the Krauts are satisfied that everything is in bester Ordnung, escort them out again.
An hour later, when the Panamanian delegation arrives, lead them to the same stash of bars.
Rinse and repeat.
If it's a question of visually inspecting and verifying the serial numbers embossed on the bars, that would require a little quick melting and re-casting, but it would still be doable.
Regards,