Can you furl it in by hand (without a winch) from the cockpit?
Have you done the swivel lubrication each year?
Are there any folds in the sail?
Is the friction in the mast or in the outhaul (try pulling the sail out directly, at the dock, with no wind)
Have you read the Selden manual?
How old is the sail?
Do you furl and unfurl in irons? (you want the sail aligned with the slot to avoid friction... ie: so it doesn't rub in the mast when you furl it in).
Do you maintain slight outhaul tension when you furl in?
Do you maintain slight furling line tension when you furl out?
Is the mast / standing rigging more than 15 years old? If so, it's due to come off, replace the shrouds and do a full inspection of the furling system.
It's a great system, but like anything else on the boat, requires TLC otherwise it starts to "misbehave".