3-Pack Replacement Gaskets for Thermos Funtainer Food Jar 10 Ounce, BPA-FREE Seals Rubber O-Rings Accessories

It fits perfectly and unlike the original seal that came with the thermos, it has managed to stay on the cover after multiple use

So far so good. Had one container where we lost the ring. It's being used today, no leaks with the replacement so far!