Have a Holt ST-200 s/n 460153 (circa 1968) which is in need of some new rubber rings for the valves. This horn does not have felt on the buttons but has a small rubber ring that is above the valve top (it kinda slips down into the valve top but leaves about an 1/8 or smaller sticking out the top) I can not find a picture of these anywhere. any help would be great , thanks