I have searched for a service manual for the very similar MG5550. Sadly it seems that no service manuals are found on the web for printers belonging to cartridge generations newer than PGI-x25/CLI-x26.
If you find a service manual for your printer, please post the link/info. It would be breaking news.
Yes you are right - I have also searched pretty much everywhere online to no avail. Maybe as time passes something will come available, and yes if I find - I will post!