The ring is less than a dollar. If you have the valve cover off remove the tensioner spring and see if you can push the rail out and that will push the plunger out also. If you can the ring is bad but you will not need to remove the tensioner body just replace the ring otherwise removal of the water neck is necessary.

The tensioner is just another thing to look at for noise at low RPM and they do fail.

The head is heavy and has two allen head screws inside that need to be removed also.

Later
Robert