I am back to share about what happened since then.
I have been writing email with Dive Rite Support since last December, describing how my XT fins cracked and when did I buy it, sharing pictures with date code on the bottom of the XT's fins.
Dive Rite Support told me they are sorry to hear about the issue. It could be covered under warranty and ask about the size of my XT's.
Now 4 months have almost past, I still haven't got XT fins repaired or get new pair of XT's under warranty.
At first I was happy to hear it could be covered under warranty, but not sure is it normal to take 4 months for Dive Rite to solve a warranty problem.
Well, if I lose patient waiting for the warranty and buy split fins, that's on Dive Rite.