Pulling things apart for an engine rebuild so I can turn the EFR up a little bit and add some more timing. I noticed that one of my intake valves is SUPER dirty compared to the others. It's the rear most valve.

 

Interesting - I don't have anything definite, but a few things come to mind - valve stem seal, bad injector spray pattern, bad seat/seal, and that valve just *hates* techron.

 

Two possibilities...
Valve stem seal leaking badly.
For that level of crap it may need the valve guide itself replaced.

Or **** poor valve seating allowing burning mixture to escape into intake port which cooks the crap out of the valve.

Really tight valve adjustment might cause this. Would have to be less than .004 cold to create this problem.
Once hot the valve might have been "closed" for too short a time to properly distribute its heat to the valve seat.
Normally this just "burns" the valve and doesn't create huge nastiness on the top of the valve.

Did you do a leak down test?
Did you do a compression test?

If poor sealing was occurring then both tests would have shown something...

The other valves looked great for a used engine.
Port nastiness looks normal for a 100K engine as well.

You should be able to find the reason during tear down...