Notos leak

In my experience, O-rings from practically any reputable vendor are a safe bet. Where it can get sketchy is with the cheap assortments sold by Aliexpress, Amazon, eBay, or similar. Even then, mostly just benign parting lines/flashing from what I’ve seen, not necessarily with the material itself.

Any time I’ve purchased specific sizes, including via Amazon, I’ve never had a problem with quality.
In cases where I need to buy small quantities of several different sizes, I usually order from theoringstore. That would be my recommendation if you want the added confidence.

https://www.theoringstore.com/store/index.php