I can think of 3 different springs in a halo.
Firstly one on the lid, secondly an anti jamp spring, 3rdly the one that goes inside the drive cone.
Did you take the drive cone off? if so it could be any of them. If you didnt its most likely to be the lid of the anti jam spring. You'll be able to tell if your lid has the spring or not easily.
if its the anti jam spring it slots in just behind the antijam beads