Choosing a Replacement Drive
The OEM (original equipment manufacture) drive was the Seagate Pipeline. At the time of writing (end of 2020), these are now only available as remnant stock. New old-stock does turn up, but unscrupulous sellers have cottoned onto the idea that the Pipelines are in demand (as like-for-like replacements; they were commonly used in PVRs including Sky boxes) and are hawking second hand units as "new" on the likes of Amazon Marketplace and eBay. They are gambling on the buyer not being sophisticated enough to check the SMART stats (which includes a log of the time a drive has been powered up for - a factory-fresh drive should be close to zero), or (worse) could have wiped the SMART stats before dispatch. That's fraudulent, like "clocking" a car to conceal its true mileage.
Almost any 3½" SATA2 drive will work, but not necessarily be optimal. For example: drives designed for general computing are required to have fast random access and high burst transfer rates. That means they will have high spindle speeds (noisy) and high power consumption. Drives designed for portable applications, where there is a risk of shock or drop, park their heads at every opportunity and might cause glitches in sustained data transfers.
Drives optimised or suitable for PVR use have a relatively slow spindle speed (low noise and power), and do not need a high burst transfer rate, but require a reliable sustained average transfer rate. These are typically characterised as "PVR" or "surveillance" (ie security camera) drives.
Summary: 3½", SATA2, 5900rpm, "PVR", "surveillance", "CE", or "AV".