Hello, all. I've been following this post for a while, and I have some good news and bad news.
Good news: I have in fact transcribed the piano intro (all 1:15 minutes of it from the original Transit Authority album) in its entirety.
Bad news: I cannot release it... yet.
I contacted Chicago's Facebook page asking if I could release the sheet music. They replied, asking for my contact info and they'd 'pass it on'. That was a couple months ago, and I haven't heard from them since. I don't know whether or not I'd be violating any copyrights by giving away the sheet music, but I am not taking any chances.
Why did I even transcribe it? Well, a while back, I bought a book called Chicago Volume 2 (Transcribed Scores). DARKWTII was in it, and the book advertised that it had 'complete note-for-note' transcriptions. However, the song starts at the part where the brass enters in.
Out of desperation, I e-mailed the guy responsible for the book's piano transcriptions. He replied saying he had the piano intro transcribed and that he'd send it to me the next day. However, when the time came, he replied saying he didn't have it like he thought he did.
My excitement (as you can probably guess) diminished (NPI) and I got pretty enraged. I asked him if he'd want to help me transcribe it, and (as you can probably guess, again), his replies sounded like he just wasn't interested so I decided to leave him alone. This was an itch that would not stop, so I had no choice to do it myself. I *had* to know what exactly was being played. It took a long time, and I did 10-20 seconds of it a day and finished it by the end of the week as a MIDI file.
I was hoping for a reply from Chicago, but it doesn't look like I'm going to get one, unfortunately. However, if I do, you guys will be the first(?) to know.
On another note, out of even more desperation, I bought an extremely old book called Chicago Transit Authority (Complete Sketch Score). What they do is take a single staffline, and fit as many instruments into it as possible. I bought a copy, hoping the piano intro would be in it, but all it says is "Free form solo piano" with a multirest in it.
And yes, this story seems crazy, but if nobody believes I transcribed it, I do have proof of it.
Hope this helps, and sincere apologies if I disappointed anyone.
Take care, God bless.
~Nick