This is the original tank from my 1975 Honda CB750F and a good example of why you should never drain the tank when you put a bike into storage. This owner did back in 1981 and by the time I got the bike a few years ago condensation had caused the bottom of the tank to rot out. It could be repaired by a competent welder and the rest of the tank is in nice shape. 40-year old gas would have preserved it.  $60. Click on my name at left for contact info.