OK - I got the Boolean subtractions to work on my original model.

1. Cleaned up my two sine wave rails (pieced together from 6 circular arrayed segments) using the shortcut RebuildCurve set at 12 points. This simplified the curves.
2. Swept one sine wave rail using a 0.014 circle. Boolean dif the resulting tube from the ring.
3. Swept the second sine wave rail with a 0.015 circle. Boolean dif the resulting tube from the ring.

One important key is the sequence of steps above: Sweep and subtract the second rail AFTER subtracting the first tube. If I sweep both rails, then try to subtract, the second tube won't subtract. So, subtract the first tube before even constructing the second tube. The difference in profile diameters, 0.014 to 0.015, is not enough to impact the render, but my guess is the two profiles can be the same size if the sequence above is followed.

Render results shown below.

Thanks for your tips Michael & BurrMan.

Ed