Or try welding in a very small metal piece on the rear sides of the deck lid, and adding a rubber stopper. I just noticed mine had this, and helps prevent the side shaking (metal on metal). When I was in AZ visiting, I saw another fine car that had this modification done as well...forgot the owners name however! See photo link below of the modification on my car which seems to work very well:
http://image64.webshots.com/164/5/45/7/527654507BgTWsh_ph.jpg
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.