help hard break pedal weak breaks after swap

It hasn't been one particular booster - I've seen the small duals and the bigger singles bad - dozens of them. It seems more that some reman factory had a bad process and didn't know for a long time, so there's just a big pile of bad ones floating around. The only way to buy an old style booster and be sure about it is to use one of the restoration shops that rebuild them in house... But its a pretty expensive service I'm told.
I don't think there's any way to track or id a particular run of them to know which are the bad ones, so its a crap shoot. I guess if they're cheap enough and the seller makes good on it, then its only a matter of more money or more time... Then again, isn't everything I guess...