Tire Sidewall problems of the 2007 BMW 335

I purchased these general tires from tirerack. Com several years ago they are rated tread life of approx 40k miles. A few weeks ago I noticed by my tire pressure sensors I had a slow leak in my front left tire. I removed the entire wheel to inspect for tire damage or cracks, and was appalled to find the inside of the tire tread had split from the sidewall the entire way around. This is quite dangerous I had no idea I could have had a blow out at any time. I do not know how long this tire was in this condition. I had approx 25k miles on the tires. I immediately ordered new front tires and did not drive the car until replaced. I am seeking replacement tire from general however they do not seem very concerned with this issue. The guys at tire kingdom who changed the tires confirmed it was very dangerous to be driving on a tire in that condition. They also said it's likely a defective general tire. General offered to replace based on remaining life but would likely find an excuse based on wear pattern and blame useage. The other front tire same brand, size and wear did not have this issue.