Getting 5D classic as my first full frame DSLR

I would use a more impact resilient adhesive than super glue (it tends to crack apart when subjected to high numbers of impacts - such as a mirror in a camera), it also tends to outgas as it dries and adhere to organic residues leaving residue that is darn near impossible to get off the pentaprism assembly - not good for an optical path if it affects you. Not to say you can't get get lucky, but the two issues make cyanoacrylate not an adhesive of choice for this application.