If you can't get it to stay together with the wax route and you can't replace it, I might consider putting on a light coat of varnish on male end of the ferrule. Letting it dry and using very fine sand paper work it down until you get a good firm fit.

It's not much different than "dressing' ferrules on cane rods. But you have to be comfortable doing this. I would do it, but the next guy might blanch at the idea.

Scott T (no risk, no reward! It's only a fly rod.)