I have been very fortunate with tires. Has one Sailun a victim of a road hazard that ruined the tire ,and this slow leak . I have no idea what would have caused such a small hole. I mean to run over something, and put that small, and that slow of leak. At the rate it was leaking 25 psi in six weeks , it would of taken 6 months to go flat at that rate.
The tires are just over a year old , they sat all winter without any air loss, took this trip this spring, and developed the leak in the one tire, its sure possible it could of been a defect . Anything is possible . Other then the one Sailun ,never had a flat tire out on the highway , its always been caught either seeing a tire low sitting in the garage ,or like this Sailun slow leak seen on my TPMS when I checked them.