The short answer is anything we could. Our philosophy has been to bring the hardest-to-get-at parts up to near new condition. Typically, these are parts not seen by most people and are such that much teardown would be needed to access them, should they fail. We have also considered cost in the equation as in the pistons which are not at new dimensions but have a lot of life left in them. Another example of trying to keep up appearances can be found with the two injector header valves. Both were cracked and could not be repaired. I made two new valves from scratch to replicate the old ones. Fortunately, this was volunteer labor, so it did not increase the cost. I wanted to save the smokebox, but it was so far gone that the net return would not have been worth it. Brake rigging will all be saved except for the four vertical levers which need to be replace to even up the brake force on the drivers.
Short story is that I hope most people will think the locomotive looks as bad mechanically as it did prior to restoration while giving years of service under steam.