I say this and I know alot will agree with me.....Why fix what isn't broken? I know it is good preventative maint.... but why mess with it if it isn't blown?! Only standing a chance then of messing something up. I say if it is running fine and you are not trying to get more boost into it, leave it alone. If it has 21k on the clock, and it's original, you have a long way to go before worrying about that a BHG. Just re-torque the gasket down a little further to around 70ish, and let it go. But to each his own. Like said above. At least 1500 for a really good job. That it mostly labor with a small cost towards the cheap OEM parts.