I have worked on a number of the prewar multi volt transformers. I do not recall if any were specifically the T, but I think they are similar. The top does not come off, it just folds back. It is tight working in side. As I recall the cord is spliced to the magnetic wire that the primary coil is wound with. The splice is taped. There may be a lot of asbestos sleeving in side. The problems I have had are there is little room to work and nothing is marked. All of the copper is corroded black. Cleaning it prior to soldering can be difficult.
Prior to changing the cord, even prior to dissassembly, check for resistance between the prongs on the plug. There should be little or no resistance. Then check the resistance between the prongs on the plug and all of the terminal posts and the case. One Megohm or greater would be nice. If the transformer does not pass these tests, there is probably no reason to go any farther, unless you can verify the problem is limited to the cord that is going to be changed.
