What glue to use on circuit board of Classe amp

That is high temperature hot glue, as used in crafts that require strong bonding. Just pop off the old stuff first.

You may want to use RTV silicone rubber adhesive / sealant. It will give good adhesion and flexibility. Clear or colored doesn't matter. It can be found at most hardware stores.

Good luck

Just buy an Arrow brand heat glue gun from Home Depot and a few transparent glue sticks.Plug the heat gun to the wall outlet and let it sit and warm up for a few minutes,then place a glue stick in the rear end of the glue gun ,press the trigger to release the melted glue from the tip in the front of the gun, and glue the parts back .
Silicone is good too but you need to wait till it cures (few hours) with the hot glue you get instant bond.
George