In this photo, the part labeled "30" is the "Valve Guide". The Yamalone I USED to own (which was Jim Thompson's instrument - i.e. heavily tweaked to his specifications) had brass valve guides where most other instruments have plastic. Why is that? Do the metal guides offer something? Do the new Yamahas have plastic or metal guides? I have never disassembled one, so if anyone can answer that for me, it is much appreciated. I don't know why, but I have a teency suspicion that having metal guides could have an affect on SOMETHING. I don't think Jim/Bob would have put them there without reason. Any insight? opinions? theories?