So today, I got motivated and pulled the turn signal apart to see exactly what was happening. Here's an overall view:
You can see that the lip on the support block which fits into the frame on the inside of the turn signal assembly is what fractured. It's a pretty thin lip. What I don't get is why the left rear doesn't do the same thing.
Here's a closeup view showing how it sheared:
Here's a view showing how the block fits into the turn signal assembly:
Looking at this closely suggests strongly to me that the turn signal stalk is not breaking because I accidently shoved it into something...the turn signal itself would also have been crunched. The break here suggests to me that the lip is shearing due to some sort of harmonic vibration or other which is expressed on the right rear side, perhaps due to different bracing on that side of the hugger. I'll order a new turn signal assembly from AF1 and see what happen...again.
Thought you might be curious..