I have a 2TB Seagate "Go Flex" USB drive that suddenly failed. Using various tools I have been able to recover about 150MB out of what was about 330GB of data.

I was finally able to run Check Disk on the drive and, after working for several hours, it completed "successfully" - but reported nearly 95% bad sectors and "unable to write to boot sector". After recovering what I could I tried saving a file to the drive - and it worked - but only up to the first 350,000 sectors or so. After that point it fails. I tried cloning the drive using several tools and that also failed with "data read errors" and sometimes "Data error (cyclic redundancy)".

So, how is it possible PART of the drive works but ~95% is corrupt/bad? What likely happened here? Is there any way to recover data out of those failed sectors or is it gone forever?

Did u sent terminal commands as m0,2,2,,,,,22 or i4,1,22 ?
If u did, that would explain why you have limited sector access.

If you haven't given those commands, you might try to clone surface in reverse direction with tools as DDRescue (Linux distro), WHDD (linux distro) or DMDE (dos), of course you'll need a destination drive of same or higher capacity that should be empty.
If you can clone only few sectors also in reverse direction, i will point to head fault or surface damage (or both).

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My firmware database:
https://mega.nz/folder/O01DkBRI

Yep, I sure did based on the numerous reports of it fixing the original problem (Seagate drive constantly "busy" and RAW with 0 bytes).

I know I was warned but it seemed to work and the drive responded exactly as described it should. Add me to the list of ignorant newbies.

Are those "bad" sectors now lost forever?

You got what you paid for.

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Luke
Recovery Force Data Recovery

I got what I could afford.

Are you a Seagate HDD engineer or factory-trained technician? Can you explain why running these codes caused this result - and why it worked successfully for others?

One can treat each and every desease with Aspirine ...

but it will help only a very limited number of them
in other cases it will not help at all, or make things worse
and on others it might kill a patient.

Several deaseases look very similar, but its the experienced
doctor to find the correct treatment - no general one button
/ one command set / one Aspirine for each and every desease
exists.....

+++

if you put chocolate in the micro wave it's gonna melt, but if you put corn seeds is gonna be popcorn

Doctors make educated guesses based on symptoms. That's what I did. When it doesn't work Doctors try something else. That's what I'm trying to do now. If the patient is dead say so. If there's a terminal code(s) that can correct the NRG-list/translator please tell me.

No, there's not

OK then. Thank you.

without tools ( PC3K , MRT.... ) is difficult to fix , you have a manual method ("Leonardo Method"/"fork method" ) but complicated

As colanco already wrote, you need professional tools to rebuild translator correctly.
Once translator will be rebuilded correctly with those tool you should get again access to all sector, unless there are other problems as bad surface on SA or weak/dead heads.

_________________
My firmware database:
https://mega.nz/folder/O01DkBRI