You can check the vacuum line to the booster for fluid inside, vacuum will sometimes draw fluid into the engine with no outside traces of leakage. If you find it, the booster needs work. If not, bleed and proceed. They are not tough, but they can be expensive. Some guys make it harder than it needs to be by worrying about the costs involved. Sometimes you have to bite the bullet and spend the cash, sometimes the system is fine.

IF all the wheels and master were leaking, the booster is likely bad too but there is no assurance of that. Old fluid gets corrosive through absorption of moisture from the air. The same fluid is in all the parts of the system and usually damages all. It should be flushed out every 2 or 3 years without fail or you will be back to square one.

Mac :{)

1962 K10 short step side, much modified for rally
1969 T50 fire truck, almost nos, needs a few things