Conchita

Hello, I recently purchased an industrial Singer 17-41 cylinder arm sewing machine. It was working fine when I tested it at the time of purchase, but now the tension assembly seems to be coming apart. I've attached some photos for reference. Can anyone tell if I'm just missing the end knob, or if the entire tension assembly needs to be replaced? If a replacement is necessary, does anyone know where I can find one? Also, if you happen to have a replacement tension assembly for sale — or know someone who does — I'd be very interested. Thank you in advance