Sticky front seat?

The driver's seat in my 2005 (130K miles) no longer slides smoothly. Seemed to happen almost all at once as though something had gotten caught in the slides, but when I took the seat out (snap off 2 plastic back covers, unplug 3 seat sensor cables, and remove 4 14 mm bolts) I could find nothing obviously wrong. The mechanism works so roughly that in the full back or full forward position I have to hit one slide with a hammer to get it unstuck. I note similar roughness in the passenger seat, but it's never gotten stuck. My wife's 2009 (85 K miles) certainly feels less smooth than when it was new. My guess is that the small 1 inch piece (1 of 2) that sits between the upper and lower track and slides back and forth almost certainly contains bearings that have lost their roundness. I have no idea how to get the race and bearings out to examine them, let alone replace them.

Anyone know anything about this? A Google search on "Prius front seat stuck" turns up nothing. Considering our second Prius seems headed for the same problem, I cannot believe this is unique!

Help!

-Ted