Same thing happened to my 79 TA hood. It would vibrate up and down from the wind going down the highway. At first I didn't know why, but upon closer inspection, I saw the adhesive "globs" had let go, so the panel was loose from the hood frame and flapping in the wind.
I used Norton Speedgrip 5 minute structural adhesive to fix it. I cleaned the metal around the existing globs of adhesive and applied the new adhesive over them and connecting to the surrounding metal surfaces. I also added some extra globs of adhesive for more strength.
The Norton Speedgrip structural adhesive is a 2 part black material that comes in a twin cartridge, and should be applied with a special dual applicator gun that dispenses the 2 parts equally together out the nozzle. So, the 2 parts mix when dispensed and hardens soon thereafter. So, you might have to buy the special applicator gun too. It looks very much like the original hood adhesive, so it matches well. This 5 minute formulation gives plenty of time to make each "glob", before it starts to set up, so it worked out great.
Now my hood doesn't flap, feels solid when I close it, and unexpectedly made the front of the hood fit better to my nose cover.