I've now posted a walkthrough for Chapter 12. I've had to split it into 2 because it was too long to fit into the 60,000 character limit for a posting. Sorry about that, as I know it's less convenient.
Someone has spotted a possible error in Chapter 11 about gettting the yellow flowers for Cocka-Cocka on the way to the Institute. To check it properly I shall have to replay that section, but I'll shall have to start from quite a bit before that, as I accidentally overwrote my save file at the beginning of that section. It may be a couple of days before I find the time to do it, but I'll try and get it done asap. In the meantime, you'll have to do your own exploring.
That, plus Christmas, means that I won't even start re-playing Chapter 13 to do the walkthrough for a couple of weeks. Also, it's going to take me a lot of work as my first play through was a mess. Does someone else wants to have a go in the meantime?
EDIT
I found a save file very close to the beginning of the trip to the Institute, so it took very little time and I have now corrected the yellow flowers for Cocka instructions. Once again, apologies for the confusion.