I assume this is your 123? Do you know if it has the updated glow plug relay. The updated one has an after glow period where the original never did and that was to remove smoking. It sure seems to be glow related to me. When you removed the glow plugs did you ream out the carbon? You seem to have conducted extensive testing of the glow circuitry but the to truly verify operation is to measure current flow to each glow plug which could be up to 15 amps each. Maybe an infrared thermometer coud be used? Antiseise is a poor conductor of electricity and should be used only on the inner threads if you had used any and not on the seating portion of the glow plugs. One mechanic over tightened the electrical nuts and the glow plugs would seem ok on the bench but installed they did not work any longer as tightening the nuts broke a connection within the glow plug.