All other boxes in the cluster are showing SQL version 8.00.2050 except one box that I have just recently added showing version 8.00.2039.
I'm not a SQL guy. Any instructions on how to bring this one to the same version level as the others would be greatly appreciated. I don't see any replication issue here though, just wanted to make sure the version aligns.
The OS SR will cause reboots, but there is no reason to do anything to the cluster. You certainly wouldn't want to remove a server from the cluster for any reason (unless you've no intention of putting it back).
You can run every server in your cluster on different OS versions; it's the version of CCM that is most important (though obviously it's good practice to be consistent and up-to-date).
So in summary - just run it same as you did before.