Looks like water has sat in that port at one time rusting and pitting the valve stem, Cleaning the port out and replacing the valve will likely solve the issue.
Oil the new valve stem before installing.......
That cylinder/piston doesn't look too good, Can you post a better/closer shot ?
Originally Posted by piston slapper
You never learn anything until you admit you don't know it all...
"Why go out preserved when you can go out beat up, worn out, sliding in sideways screaming, Holy Sh!t What A Ride" !!!