Don't have a 400 BUT, on a 350, the vacuum line should be hooked to the rear of the intake (see picture link) and have a loop that rises above the carb level to (I think)keep gas out of it . By "screwed" if you mean there is a screw in it, then the trans won't shift till very high speed like it was at WOT (Wide Open Throttle)
The rubber "Repair" hose in the cooler line is typical because it's faster to cut the line then remove it. This is NOT factory but should be OK once you replace the hose.
The kick down cable can indeed leak. I think there is an O ring but I don't know for sure.
Leaks are so much fun, mine turned out to be A CRACK IN THE WELD ON THE TORQUE CONVERTER after resealing it and replacing the pump didn't help.
One of the tubes you mention may be the filler tube / dipstick? That should be secured by a trans to engine bolt at the rear of the engine.
Good luck, I'm sure others will have some more suggestions.
Bruce
Vac tube or line on a 350/350