I cut the patches and skived the edges; then cut Vs in the bottom edge of the patch so I could bend it around the bottom of the flap evenly. I glued the patch to the saddle, clamped it, and left it to dry. Then, I started sewing. I followed the original stitch lines, but skipped every other stitch in an effort to stress the leather as little as possible (lots of little stitches means lots of closely-spaced holes, which isn't a good idea when the leather's compromised ... which this leather definitely was!). The existing seams were a bit uneven, which translated into the stitch lines being a little crooked, but I kept telling myself that function was the important thing here(as much as it galled my rather obsessive-compulsive soul).
Next, I cut patches for the panels, skived the edges, and glued them on. No stitches, since I didn't want to sew all the way through the panels, and the panel leather was too tired to tolerate them (if you look closely at the underside of the flaps, you can see the V notches I cut):
The saddle went home this past Monday night, hopefully to have at least a few more months of exercise rides. If there are any more problems, however, the owner really needs to invest in a new saddle.