You were right about the plastic parts. One was shot. Put two new ones in and carefully lubed up the mechanism with some waterproof marine grease.

Also discovered that you can adjust the stablizer bar that stablizes the "scissor joint" to the door frame. Put a bit more tension in that and *wallah* - good as new.

Shot some silicon slip spray on the tracks for good measure.

Bet it'll be good for another 15 years.

thx

Jeff