Odd Hard Drive Problem

I'm trying to fix a 9 year old Sony SVR-HDT500 video recorder which contains a 500 GB hard drive optmised for video recording.

The fault symptoms are slow loading of menus and jittery playback. I removed the hard drive and checked it connected to a PC. There are no obvious errors but the transfer rate is very slow which would explain the fault symptoms. I'm assuming the disk is beyond repair unless someone has a bright idea.

I would normally install a new drive but Sony have cunningly linked the serial number of the hard drive to the serial number of the mainboard requiring bespoke Sony software I don't have to register the drive before it can be used!

Don't know if this gives a clue-
Sony RDR-HXD970 Hard Drive Upgrade - YouTube
from about 6 mins on it refers to a 'service remote' (controller) - used after inserting the replacement drive...

My interpretation of the service manual was wrong and you can simply replace the hard drive. I replaced the original drive with another similar drive but of lower capacity and the recorder now works as expected. It seems my original diagnosis of an interface problem in the original drive causing a slow data transfer was the problem. What hard disk problem would cause a SATA hard drive to pass the error checks but transfer data very slowly?

There are quite a few threads here on
low transfer rate
associated with
100% disk usage