iMac hard drive replacement

Apple has expanded the hard drive replacement program for certain 21.5- and 27-inch iMac computers.
This is the second time Apple has extended the program, including more computers each time.
From the Apple support page:

Apple has determined that certain Seagate 1TB hard drives used in 21.5-inch and 27-inch iMac systems may fail. These systems were sold between October 2009 and July 2011.