Keep in mind that you don't have to remove *all* the old adhesive, just the loose stuff. It's sufficient to scuff up the surface with a Scotchbrite pad so the surface has adequate "tooth." (A 3M thread is emerging here!) My personal experience is that the pad is what fails, not the adhesive.

Adhesive: I've used 3M Super Trim Adhesive, N. 08090. It comes in 19 oz. spray cans and is specifically recommended by 3M for hood insulating pads (says so on the can). If you follow directions for application you'll probably need a couple cans of the stuff. It runs about $12 per can.

Russ M.
'82 300cd (new hood pad, 2001)
'82 300td (new hood pad, June 2004)