Pulled the plug from the engine that showed the low temp header and to me it doesn't look too odd, not like something major. Need to get to the store and put in a new one to test that first but Orileys only has the APP3923 (link below) rather than mine in the photo (3923). A bit different looking on the electrode part although threads seem the same.
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.