Are we talking about a fuel leak here or a coolant leak? If its fuel weeping from around the Injector pipe locking nut it could be a crack around the pipe union as it locates into the Injector, or the pipe itself has worn/cracked, check any part of it for rubbing against something, fuel can run from a place of leakage quite a distance from where it shows up, if its from the Injector where it fits into the head then the sleeve and seal could be suspect. I’m doubting this is a coolant leak just by what the OP said but if it is running the engine until full operating temp will usually show where its from or do a coolant pressure test. Not sure I’ve heard of an air line crack though! 
Franky.