It is possible this is one of the very early Fenwicks before the tip-over-butt ferrules were developed.

The early ferrules were a larger piece of graphite that was slipped over the bottom of the tip section and glued in place. The top section of this piece of graphite was sloped down to the tip section to create a good transition between ferrule and tip section.

If this is one of those ferrules I would recommend wrapping the sloped section from ferrule to tip section.

I hope that makes sense. It is hard to describe without pictures. I have not seen one of those ferrules since the early 80's.