I still have one of the original Chinchillas that prompted me to start Chins & Quills, she is the Beige Chinchilla in the CnQ logo. She is about 23 years old now, still running on a 20 year old Leo Braun wheel.
She and another Chinchilla that I "rescued" have been eating Purina Show Rabbit food for at least 10 years now. I don't know what else to offer but I do believe it really comes down to genetics. She came from Maryanne Holden in Encinitas and has a curly tail, like dwarves do, but isn't a dwarf. She did have a dwarf baby once though, which unfortunately did not live that long. She has had 5 kits over her lifetime, the last must have been 16, 17 years ago.
That is AMAZING ...Can you list all the brand names of the company and products you are using? I agree it's genetics to an extent. But diet and exercise contribute a good deal to your Chin's health. And remember, LOVE is one of the most critical factors in the health and longevity of any animal in our care