Whats wrong with my brakes power booster?

1965 polara, single pot res. Pedal is firm both with vacuum and without. I can pull the plug on the canister where the vacuum hose attaches right after I run the motor and get a hiss of sucking air into the canister. I dont think I have a leak but I am not getting any power assist. Time for a new PB ? I just bought this one 5 yrs ago with barely 5k of use.

Here is a sheet on how to test your booster. see attachment