I am in the middle of a complete rebuild on my 99 YZ400. while I have it torn apart I decided to remove the valves and port the head. After inspecting the valves I found some light pitting. As cheep as valves are I would rather replace them. Do I need to take it to a machine shop to have new seats installed or does it need to go to a dealership. And do the valves need to be ground or can I just lap them. And should I replace the valve guides while it is apart.