I haven't taken the hose off yet to see if the plastic underneath is cracked, partly because I couldn't find a drain cock to lower the aintfreeze level so as not to spill antifreeze all over when I pull the hose, but after I made the post, I went out and looked again. When I first detected the problem, I could wipe my finger under the hose connection and come up wet. After re-seating the clamp and really cranking it down, no more moisture at the hose. But...there was a new and larger puddle of antifreeze and I can see wetness in the recesses where the top of the radiator is connected to the main portion. What I think happened is that sealing the hose leak pressurized the system and started the leaks elsewhere. I just drove over to the local auto parts store, and poored in a can of radiator stop leak after the manager's advice that so long as the heater isn't active, I was running no risk of plugging up the heater core (I hope). So we'll see what happens over the next few days.
Since I don't have a rack I'll have to get the wheel jacked off the ground and start jerking on stuff to find whats loose still, but with two mechanics saying they can't spot it, I doubt I'll have better luck
As to the vibration, no I can't really tell. A 280 motor isn't particularly quiet, and when that old A/C compressor kicks in it adds noise and vibration too. But with the compressor off, the vibration and subtle brrrrr... is still evident at roughly 40+ MPH