Ok so heres the story, on a new Apple iMac you get a hybrid setup SSD + 1TB Seagate Drive. The SSD makes its quick and the 1TB is for storage.
Trouble is that the "1TB DM" drives that apple are putting in these machines are terrible. (the 2+3 TB ones are the worst) but these are still bad. And they fail in high numbers
One of my apple contacts down south had an issue with one of these drives and asked me to get a clone of the bad drive. I Imaged the drive as best I could using the heads that came in it and then decided to change them.
Here are some images and a video of the result of filling in the missing data on fresh heads.
On these drives I like to match the first 3 on the serial, in this example its S1D