I’m customizing the FLVPlayback component with the individual video control components, but the SeekBar wouldn’t work no matter what I did, though the PlayPauseButton worked fine.
vidPlayer.seekBar = controls_mc.seek_mc;
Turns out that you need to set the SeekBar property of the FLVPlayback component AFTER you call play().
It took me a while to find the resolution to this annoying issue; hopefully google will index this post and help someone out.

Found your note via Google – just what I was looking for. My project has to be finished tomorrow and this was the final stumbling block.
Many thanks, Geoff
BTW, I found you can set the seek (and volume) controls in the AutoLayout handler, rather than waiting for Play to be pressed (handy if you have autoPlay turned on).
myFLVPlayback.addEventListener(AutoLayoutEvent.AUTO_LAYOUT, layoutUpdate);
function layoutUpdate(e:AutoLayoutEvent):void {
video.seekBar = myControls.seekBtn;
video.volumeBar = myControls.volumeBtn;
}
nice! — thanks for the tip