@buster80: I agree with
microsoftengineer that one possible (likely?) reason for the behaviour you describe, is that there is more to this story...

Here are some brief specific questions:
buster80 wrote:
1TB WD10EADS
What's the history of the drive? Where did it come from (enclosure or not)? What's the original reported fault?
buster80 wrote:
no partition info in Rstudio/UFS
What does LBA 0 actually look like? Recognisable MBR code or not?
What does LBA 1 look like? All zeros? Or a repeating 16 byte pattern? Or something else?
buster80 wrote:
data visible in winhex - unpartitioned space
But is it
recognisable data (text / jpg / etc.)? Or does it appear to be random (and therefore possibly encrypted)?
buster80 wrote:
not encrypted apparently
What leads you to that conclusion?
You might find this thread interesting, if it turns out that this drive is from an encrypted enclosure, as it shows some of the behaviour you seem to be reporting e.g. no valid partiton table on the bare drive (because it's encrypted by the enclosure):
http://forum.hddguru.com/disk-with-sata-usb-adapter-remove-virtual-rom-t18492-20.html