It just so happens that I am working on an F2 right now so I got some pics of tappets. Unfortunately, I could not get pics of the valve stem as I am not taking the head apart right now. These are from a bike with 16,000 on the odo, which I have no reason to doubt. I ended up replacing 4 of the 8 tappets with better ones from a scrap K3
The ones I left alone looked like this.
20180923_144833 by
Sean Barney, on Flickr
Here is one showing one big pit. The associated valve stem looked ok peaking through the inspection cover and down through the empty rocker. The valve clearance was still correct or close.
20180923_150801 by
Sean Barney, on Flickr
This one was associated with a pitted valve stem tip and was chewed to hell with over twice the recommended valve clearance showing.
20180923_153945 by
Sean Barney, on Flickr