The white color might indicate hot/lean. The buildup on there is probably a lot of gasoline additive. But maybe oil ran down from above and burnt on the stem.

To save money, just use water. It should hold water overnight. However, with that buildup I would disassemble the valves, clean the with a wire brush on a drill, and then hand-lap them back in. If it doesn't hold water, they should be ground on a machine.

Also check the valve side-to-side play. If there is any play have new guides put in. I didn't have much success with kurnling the guides.

I recommend the umbrella style of oil seal (ford-style) that ride on the valve like an upside down thimble. The positive seal type that fits over the guide seem to pass to much oil except when the guides are brand new.