The Day Sailer II needs to have constant tension on the CB cables to avoid them slipping between the CB and the side of the trunk. All later-model DS II's have a length of shock cord on the uphaul that keeps the slack out of that cable when the board is down. I agree with Sunbird that there is something amiss with your downhaul cable, as it rarely jams. The original through-deck fitting would hold the cable on the pulley, and the cable is always being lifted away from the board.
I'll make another guess--I suspect that the tang (the metal strap that fastens the cable to the board) has become twisted, so the cable is no longer centered in the trunk. On the older DS II's the two cables (uphaul/downhaul) cross inside the trunk, with minimal clearance. One tang is mounted slightly to starboard, the other slightly to port. Any bending of the straps might cause a foul. The definitive cure is to drop the board, find out what's going on, and fix it.
For what it's worth, I think the older system is better than the rope/block&tackle system that replaced it, so I think it's worth fixing. Check out the daysailer.org association forum for exhaustive discussion of CB issues on all versions of the DS.