Burnt/Pitted Valve Stem

Howdy!

I got a v6 Camry engine and I've noticed that the right hand side exhaust valves (all 6 of them, by equal measure) are showing signs of pitting/erosion on the valve stems. Anybody know why this would happen to the right hand bank only?

Also, if the burn-off isn't severe, is it still safe to re-use the valves for a couple more years? I have a 92 with more than 120K miles on it, I'd hate to spend on new valves if something else in the block is gonna call for some major work just a few more miles down the road. I don't drive the car hard anyways, so unless I purposely set the timing late, the valves should hold up for a while.

Thanks for your advice!