As for my hearing, , to quote Uncle Louie in Christmas Vacation, "You couldn't hear a dynamite truck in a nitroglycerin plant" would closely describes mine. After all, I drive a Defender
If you want, you could use the hose from the engine end and check the hose too.
The parts are in this order engine, hose, 1 way valve (plastic & held in a rubber gasket/grommet to the boost chamber). Check the hose for cracks & wear/rub spots. If it needs replaced, NAPA has vacuum hose by the foot. It is stiff walled and will not collapse from the vacuum pressure.
The amount of vacuum you list is correct to hold.