I typically try to ensure that all drive axles are oriented with the north magnetic pole in the same direction. There should be three or four of those loose magnet inserts in the hollow axle. If you only have one, the magnetic effect will be very limited. I would probably not even bother putting it back in.
Before you start using Loctite or other adhesives, you may want to try crimping the knurled ends of the axle fittings in an effort to get the parts to fit back together tight with a clamping/friction force. Loctite may not be a problem, but some adhesives that sheet out, like Superglue, will actually form a conduction barrier film, preventing reliable grounding of the locomotive. I learned this the hard way many years ago when I tried superglue on loose drivers only to discover it's insulating properties.
