The Favorite action has no spring or direct means of keeping the lever in the closed position. It depends on the tension of the block against the barrel and the fact that the link pins and the lever screw are past dead center when the lever is closed. The problem is that if there is wear, either at the barrel face or in the linkage, the finger lever flops loose.
I have no idea what brass part Thralldad is talking about, but possibly it is something installed by a previous owner or a gunsmith to take up the slop in the linkage. There are no brass parts in the original gun.
Jim