I finally decided to take the jump and replace Mirella’s iMac dead HDD myself.
For all I read, it is not a trivial operation, but not impossible either; I am actually lucky because on newer iMacs the bastards at Apple are making nearly impossible to DIY repairs by fitting their hard drives with thermo sensors in the disk chassis, custom firmware as well as non-standard pentalobe screws!
If you’d like to get a feel for the surgery, I will be following Brian Dorey’s excellent video guide:
Point of no return was crossed five minutes ago when I ordered a replacement hard disk; I will take this opportunity to replace the original 250GB with a massive 2TB SATA II disk which should give a lot more room and a small performance improvement. The website said it will be delivered in a couple of days, so over and out until the package arrives.