Added spring on Shires axial valve linkage?

[DCIsky]

I currently own both a custom Shires axial-valve tenor trombone and independent bass trombone, compiled through buying and selling parts (so presumably none of these parts were originally sold with the same horn/batch). My tenor's axial valve has a unique spring on one of the bearing joints, and (as far as I can tell) it applies pressure to the bearing joint in order to reduce any play within the mechanism. This happens to be the quietest and nicest-action Shires axial mechanism that I've tried (especially compared to my bass valves, whose linkages don't have this spring). I bought it off eBay from a fellow in France, so I don't have much information on the valve, although it looks to be fairly new, with none of the lacquer loss that has plagued my other Shires components older than 7-8 years. Is this now a standard component, or is this an aftermarket installation?