Most of you know of this part, its the 2 hose piece that goes to the heater core through the firewall....Make sure you do it, i got lucky it started dripping in my street and i smelled it before i left. So for all you swappers or anyone over the 100k mark really do it when you get a chance or be ready to pull things apart. I was told to do this when i had the motor out(i didn't) it took about a year and a half but it went out on me.
I probably didn't have to go this far but i did a little cleaning as well as a water pump and thermostat housing, and i also found another plastic cooling piece that was broken its for the M5x family of motors though, it connects 2 cooling hoses together replaced that one with a metal piece now.
Its cool though as I'm redoing my whole vacuum system and really cleaned the motor i might get the knock sensors done at the same time, but its a bit pricey right now.
Cheers! and happy new year!