You guys are amazing at your work with GM cars. Definitely will be sending folks your way to work on their cars. Especially DTS suspension and head gasket replacements.
A little late to the party but you do not want to touch any electrical connection with your finger because of natural skin oil. You also want to clean the fingers in the plugs. You should always clean the file spotlessly or use a new fine fingernail file board. Creating more pressure by raising the solder is a bad diagnosis and a poor fix. The solder did not evaporate over the years. The contact points simple oxidized. SprayClean and Q-Tips first, then fine polish and solder LAST.
