This one was a major PITA but I did get it done. Installing the retainers requires partially disassembling the door, which requires removing the door altogether. So the first step was to separate the door from the three wheels at the top. In my installation, this required removing one screw for each of the three rollers. There was a lock nut at the top, and the axle for the roller was also threaded, so after removing the nut I had to unscrew the screw from the axle. (One of my screws was bent, so in order to get it out I had to drill out the pop rivets holding the roller trolley to the door frame.)
Once you've go the door out, it's an easy matter to remove the bottom extrusion from the door glass, and then slip out the old retainers and slip the new ones in. The screws have a #1 square head (not blade, Phillips or Torx), so make sure you have one in your tool kit before starting.
This took me about three hours, but if I had to do it again it would probably only take about one hour, now that I know what I'm doing. Hopefully my post here will be of some help to others.
