I'm pulling the heads, and when I pulled the middle portion of the intake manifold, I had a bit of anti-freeze in the intake runners of the lower piece. Anybody else ever see this before? I've been losing coolant for years now, and I wonder if I've had some unintentional water injection going on.

I've never seen that before.... perhaps the throttle body has a crack where the preheat coolant lines go in? I don't know if that would be a possible way it could get in or not.

Yep - that was my first thought - coolant from the throttle body. I think, if the gasket between the throttle body and the upper plenum fails, it can leak coolant into the airstream.

My memory tells me that keeping the coolant passage in the throttle body a "closed loop," depends on that gasket.

That just reminds me how much cleaner my intake looks since I removed all of the TB cooling lines and hoses. You have no idea how much space all those lines take up until you see a car with them removed. Same with the EGR Pod and EGR Pipe. (and yes my car does pass emitions)

I was thinking about the TB leaking, or the intake having a crack. The intake looks good, except for all the carbon in it. I'm taking the heads to the machine shop today, to be decked and reseat the valves.
My cylinder walls are beautiful; hardly even any ridge at all, especially with 171,000 miles. Maybe those 2500 mile oil change intervals were worth it after all.