As evidenced by the rapid change in clearance, your exhaust valves are shot. It's the seat face of the valve that's giving up from the hot pummeling it's taking from too-hard exhaust seats. I bet you a doughnut your exhaust guides are finished, too.
Valve guides are a whole $10 for the good aftermarket pieces from CC Products.
If you're going to take it all apart to change the exhaust valves, I wouldn't mess around with it. I'd change the exhaust guides, too.
Your intakes, valves and guides, are probably fine. They run nice and cool and properly adjusted last 4-ever. Almost.