The i9900 does not go together with screws and bolts, at least in regards to the housing, the way any freaking decent printer dang well ought to.
IT EFFING CLIPS TOGETHER.
Cue me, hunched over a table with every friggin slot screwdriver in the house, back screaming, literally prying the piece of $#!* apart because that's the only way in.
IT TOOK OVER HALF AN HOUR.
Dear Canon, while I understand that there must have been some sort of budgetary pressure requiring you to shave fifty cents off the manufacturing cost of each printer -- DID YOU FREAKING HAVE TO DO IT THE GOLDANG *STUPIDEST* POSSIBLE WAY...?!?!?!
I now know two things very well. The first is a rather considerable litany of curse words that do not exist in the English language. The second is that at least my next two printers will very certainly NOT be made by Canon.
Ironically, I may have fixed the mechanical issue in the donor printer, after getting the shell off. The intake hopper's roller was stuck in a particular spot and I did knock it free. Once my blood pressure and heart rate return to sensible levels and I can look at it without starting to speak in tongues again, I think I'm going to swap the printhead and ink cartridges back into the donor machine and see what happens when I apply power.