I really think it is the o rings, if I had the money to have proper tests done I'd gladly do so, and wager a hefty sum on the o rings as being the culprit, in the case of leaks anyway.

And I'm also pretty sure the Dorman o-rings would deform, or as ole fart said, "form to the walls and notch, and aren't round anymore" that is what I noticed when mine leaked and I changed the o-rings, the o rings were no longer rounded as they were before.
I'm willing ti bet the Fel-PRO'* I put in have not done that, which is why they have not leaked on me yet, I've only put around 1,000 miles on it so far though.

As for the elbows cracking, a lot of them do that if they have been in there for a long time, I think it has to do with a combination of heat, and of vibration over the years.