It is called a voltage leak. There is electricity feeding back through the machine from a short. Don't use it until it is fixed. Replacement parts are indeed cheaper than postage to a reputable shop. If you have an electric tester, check the machine at various places where it may be leaking from poor or cracked insulation. Your husband can do that without removing parts, only inspection ports etc. THen you will know if it is from the foot controller or the machine itself. It can be visible on FWs. The wiring doesn't age as gracefully as the machines. It was made froml rather primitive formulations of rubber.
You don't find many lamp cords of that age that haven't been replaced. Just remember or number the terminals when he replaces the cord, if needed. If he is as handy as you say, he already knows this. Take pictures and post them to Billy and he can advise you if it needs to be shipped for repair though.