The disconnect is made by Becker, the part is called the "Cap Washer". The cost is 25˘. you should be able to find this at any LHBS or online. The are sort of a square edged O-ring, so you standard hardware may not have this kind on hand. You will also find that most seals/o-rings in the beverage industry is a material called EPDM, which does not impart taste or odor.
if you need, we could order the part and mail it to you.
Tom's Brew Shop.com