It may have been at one of the swage fittings, or my memory may be fogged by time, and the failure may have been due to weakening of the wire after a lightning strike. Still, the loose rigging allowing the mast to move side to side didn't help.
Backstory: In late June of 1985 while owned by the previous owner, my DS II was apparently struck by lightning. The bolt went down the mast and exited through the bottom of the boat as far as I can tell. Part of the electric charge also travelled down the shrouds (not sure about forestay?) and the heat of the electric charge actually fused the strands of the cable (3/32") together at the point where they pass over the tips of the spreaders. One shroud snapped while under sail, I think the owner replaced the broken shroud (with 3/32" cable). but not the other side, which broke later due to the shock-loading caused by the loose rigging allowing the mast to sway as the boat rocked on the mooring.
However, my memory is unclear now as to the exact sequence of events and now I'm faintly recalling that he replaced the rigging at least twice...... So, the 1/8" rigging that is there now may actually be the 3rd set (original 3/32", replaced with 3/32", replaced again by 1/8").
But even if the looseness didn't cause any of the rigging failures, it certainly did not do it any good.