I agree- it's a flimsy spring so doubt it's tied to the set screws on the shaft but it was odd to find it at the same time of the incident when I know it was not there previously. Rick- the previous owner did seem to replace the aft transmission seal a few years ago. However, the transmission is essentially in a separate section of the bilge from the shaft and the set screws. Or stated a better way, there is a bulkhead just at the junction of the shaft and the transmission so if something fell off the transmission it would tend to want to be on the other side of that bulkhead and not under the loose set screws. And when I say loose...I don't mean just loose, I mean both set screws completely worked themselves out and were laying loose on the bilge floor next to the spring.
It's such an odd shape and such an intentionally made part that I kind of feel like it probably ought to go back where it belongs, if only I can find out where that is!