http://www.google.com/patents/about?...tent:1,219,964
Found this link to patent# 1,219,964 which is the Lefler SST that Parker used. Its the early one dated Mar 1917. Same as what is stamped in the gun.
Slightly different looking in the gun than the illistrations. I guess Parker made some modifications after they purchased this patent.
Looks like piece/ part #38 the leaf spring that acts upon the detent is the one I am looking for.