Thanks for the link, Keith. Obviously I'm not the first one to observe this.
I just got off the phone with Dexter's California plant, and they said that "hairline cracks" are signs of normal wear, and are not cause for replacement. She mentioned the info was on their website, which I find unneccessarily difficult to navigate, but I finally found it on page 16 of this PDF (page 12 in Adobe):
http://dexteraxle.com/i/u/6149609/f/...rakes_6-11.pdf
I've also attached the PDF as the above link has broken in the past.
So, I think I am comfortable with that, and will leave them on there until next year's inspection.
Dave