Remove the hose going to the brake booster and plug it off. If that makes a difference there is prob a leak in the diaphram.
Spraying the hoses and connections with soapy water only works with pressure coming out , not vacuum.
Try taking a propane torch , UNLIT !, and apply the gas in small amounts to the vac connections with the engine idling , any change in idle will pinpoint a leak.
Take your time and don't wear loose clothing.