Others will be more knowledgeable, but in the meantime, I would check the following:
1) Shroud tension should be fairly tight--too loose and it will not furl properly
2) Halyard tension should be taut but not too tight, just enough to get the horizontal
lines out of the sail, otherwise it may be hard to furl
3) Make sure you don't have halyard wrap at the top of the
furler
4) I would take the sail down to get at the top fitting, and spray it with McLube and ensure it swivels freely
5) Ensure that the reefing
line and the blocks it runs through are smooth, operate freely and at the right angle
6) Ensure the reefing
line is the correct diameter/thickness so it isn't binding in the drum or rubbing on any part of the drum as it furls/unfurls
7) Unscrew the fitting just above the drum (3 screws, i think) raise it up a bit, lubricate it with McLube
If all of that is good, spray water into the drum to rinse off any salt and then spray McLube in the drum itself where the bearings are to lubricate it. If that doesn't solve it, I'm not sure.
Good luck!
Frank.