Well, this is a pretty simple system. If the step has not sunk and the attachment points (stemhead and aft chain plate) are intact, then one or the other of the two wires involved must be longer. Visual inspection
of the backstay is simple, and you have likely had a look at it already as you put up the mast. This leaves the forestay as a likely culprit. Most of it is inside the furler
and hard to see, and there may be a rigging
screw inside as well. Have a good look there... if there is a hidden rigging screw, it may have been unwound a bit, or the wire may have stranded and stretched enough to loosen things up.
Also, have a look at the tangs on the mast where the wires are attached. Don't know how Tanzer dealt with those, but some masts have them bolted or riveted in place, and the fasteners could be loose or failing.
There are not that many places where things could have changed...