You saying it's bad where the center contact ring contacts the rheostat coil end?

I guess I'd try chemical cleaning:

http://www.dodgecharger.com/forum/index.php/topic,70039.0.html

Vinegar and salt works great but you must rinse well as stated in post #6...... "Flushing out with water then treating by spraying alcohol in the connector is giving a stable finish, my reading up proved you need to halt the posses or the copper will corrode (oxidize) even faster drying out."