FICUS PRODUCTS of Hamilton, OH have come up with the perfect fix for the "S" hi-rail knuckle coupler problem of inadvertent uncoupling when operating with rolling stock.
Please take a look at the bottom of the page at
http://www.lbrenterprisesllc.com/FICUS-PRODUCTS.html
The STA-COUPLED is a very simple fix at a more than reasonable price.
Dave, LBR