Hi guys,
Purely to ensure this thread stays factual. The Seagate hard drives had the EOL notice raised in Dec 2019. See doc below from Seagate confirming this.
We can’t buy parts of dubious origins from EBay etc. - on official repairs we have to use parts that we can trust where they have come from and haven’t been used etc already.
As mentioned before, we do support these servers and they are a very old design - one of my first projects back in 2006 when we did Naimnet 
if a DIY fix is wanted, then one way forward is to clone the drive off another HDX server. The default device name won’t be right as won’t be paired to the motherboard correctly, but it will operate assuming no other faults on the product.
Best regards
Steve Harris
Software Director
Naim Audio Ltd.