I suspect you will find more lifters that look just like that one if you pull them out and have a look. Once the wear gets down past the surface hardness (see the ring around the outside?), they dish pretty quickly.

Time for a new cam and lifters, or you can install new lifters, then in a couple thousand miles, when you pull down the motor to clean up all the metal partials, you can buy a new cam and lifters along with the bearings and everything else the metallic oil has flowed over or through. Gene