bobstro

To do this with a vector gradient you need to use the Fill tool. That gives a lot more control over the start and end points of the gradient.
 
If you use Effects, that will produce a raster gradient which will always be rasterised on export. So it's usually better to use the context toolbar or the Gradient tool.

For the sake of covering everything, you can also force rotation in 15 degree increments by holding shift as you drag the rotation handle. If you cover all of the sub-15 increments and use this rotation with duplication, it will be spot on.

Your tips worked perfectly. The cog is handy for quickly placing things visually. The trick of grouping objects so that the center point is located on the hub is the key.
 
Here's what worked:
Create the 1st marker as a vertical line in the 12 o'clock position. Duplicate it with Cmd-J Rotate the selected copy holding the shift key to restrict it to 15 degree increments into the 9 o'clock position Power duplicate the copy 2 times to create the 6 and 3 o'clock markers, giving me a set of 4 perfectly aligned markers Select all 4 and type in 1.2 (or 6 or 30) in the R box on the Transform menu Power duplicate like a madman with Cmd-J I turned off the original 4 markers and was delighted to see the final set of duplicates come to position at exactly the 0, 90, 180 and 270 degree positions. It's not intuitive, but it works quite well now that I know the trick.
 
I think the cog will simplify another challenge I had using GIMP in aligning elements on the face. I'd create a circular guide line, some radial lines and try to align on that. Using the cog, I'm hoping I can easily snap to geometry much more easily.
 
Thanks A_B_C & Dale. I'm really enjoying AD and this has helped get past a real stopping point.