70 C20 Hard to Brake

[CW4B]

Stopping hard one day. Thought maybe vacuum booster? Hear vacuum leak in area around vacuum booster. Shot some starter fluid around area while running, no reaction. Disconnected vacuum line from booster and hear no vacuum leak as before. Anything else I should check before determining vacuum booster is leaking internally? Also, this is a rust bucket presently, including the booster and m/c. Perhaps trying to repair vacuum pump isn’t a better idea than repacing?