However, I have one problem with it. One of the halves has a pretty significant bump in the center of the cap, rather than a fully concave surface, like on the other half.
Is this normal for classics? Did I get a bunk one?
Give it a push… Does it give at all? If you can push it in, then I’d just imagine the caps just sit tightly… If not, maybe that’s where part of the axle sits and pushes on it?