I just had my spring housing out too, I am in the same process as you on replacing bearings on the upper spindle on a 57 greenie, and cleaning it up. In the process the quill hadle was not locked and the spring unwound and became disconnected from the pin. BUT my spring is "1" piece, the key lock end is part of the spring. I wont say your end is broken off because in the pic it is so symetrical, the "ears" on both sides of the small piece. I have seen 2 pieces that have ears like that and interlock under "pull apart" tension, but not on a spring in a housing like that. It seams/looks impossible to do that, then lock the piece on the pin, and get it all (main part of spring) under tension again once installed.
I wonder if that piece broke off uniformily, for what ever reason. I am not an expert and have no real experience with springs and the type of steel that is used and how to work with it. Mine was as clean as your pic when I opened/removed the shaft it sits on. I do know this, that springs of that style, when wound and all the "layers" are tight against each other, can rust together, if not being used for long periods, depending on humidity or H2O contamination, (wound tight, then unwound), if it does not have a light coating of some type of lube/anti corrosion substance on it.
Some how I thought in a previous post you mentioned you were "Down Under", thats why I asked about the nationality, a bit of the Irish in me too, best side!!!
Measure once, cut as many times as needed to get it right! Bob
56/57 Greenie with jointer, 85 Mark V with band saw, 63 Goldie with jointer, 3 ER 10s, 1951 vintage, Hernia from the Er 10s, Tool Shop SS clone 6" jointer, and 6" belt sander, Delta 10" TS, Buffalo 6" jointer, Craftsman 12" BS, 10" Ryobi planer. Compound Miter, and misc.