I have noticed cracks on the red o-ring a few times. Didn't experience any leaks from it, but I replaced them anyway -- might not have been necessary, but I didn't trust them like that. The two times it has happened to mine, it has been in periods where I was half-assing my post-dive maintenance routine. So I think it either comes from sitting in the sun, or from not rinsing saltwater off sufficiently well. Now I give them a fresh water soak after each dive, and dry them either indoors or in the shade, and I haven't had cracks in a long time.
I do spit on or lick the red o-ring before inserting the glove side into the cuff side. Can't remember where I learned that trick, maybe here on ScubaBoard. Makes it easy to doff an hour or two later, every time. And, I do lube the red ring occasionally, maybe every 6 months or so. But, I was doing all of that when I was getting the cracks too, so I blame poor cleaning rather than poor lubing.