I enjoyed your story, minus the #4 nightmare of course. I feel your pain, but I am also glad that you are in it to win it man. It looks like you have the $ to play, but it still sucks that you have been given the run around a bit.
After I bought my car (of course) I started looking (still do BTW) for WRXs and STIs every place I saw one sitting on a lot. Just looking.... I kept noticing one thing that kept poking me in the eye; I kept seeing a bunch (most) of the 08+ cars and even a lot of 05-07 ones sitting on lots with VERY low mileage. Anywhere from 8,000 miles to the low 20s. A lot of them. I started (and still do) wondering "why are people trading these things in with such low miles?" The cars look to be in immaculate condition, so what gives? Most would have had to have been upside down still with such new cars. I even have asked some sales guys what is up with no real answers. I have my own theories. Do you want to read them? Good. I think a lot of these cars have been blown up or something, folks get the warranty work done, and then just say eff it and trade them in. I suspect most get blown up by "kids" trying to be Ken Block or something doing AWD redline launches and trying to drift the things in parking lots. Not all though. Now, this does not make me feel good at all. A lot of the guys on here that have been working on these cars forever say that the Subaru reliability is a myth with the turbo cars, and always have been. I don't want to believe them, so I won't. I guess that the N/A models are pretty reliable and that is where the myth is propogated. These engines by design are not able to handle 300HP+/- safely I am told due to the small rod and main bearing surface areas, along with some rod bearing lube defficiencies, "bad" factory tunes, and blah blah blah. They are not big ole V8s for sure and are already wound pretty tight from the get go. That is one reason I have stayed stock, minus the Stage 1 fun I have with my AccessPort. I have an 08 that I just turned 67K in and have not had any internal failures (knock on wood). I am a maintenance OCD person and it sounds like you are too. I could be just lucky I suppose.
I think you are right about them just wanting you to go away. It would seem to me that a blown piston would indicate another problem and at lease rate a good solid honing of that cylynder wall. Leaving all those bolts out would have set me on fire because it shows that they really don't care. Get that baby built up and have some more fun.
When I saw "2008 STi in Oct 2011 with 18,000 miles" it made me have to ramble as well because I thought about all the cars I have seen with that same low mileage sitting on all hose lots. I also thought out loud I think "How could anyone have one of these cars and only put 18K on it". i can't say out of my lowly WRX. BTW, I went with a WRX because I don't want too fool with all that electronic wizardry and witchcraft that is the STI ten years from now because I am keeping this thing forever, even if I blow it up tomorrow.
Good luck to you and keep us posted. I hope that I made you feel a little better by rambling right here with you.
Ramble on brother.