WD "Blue" drive not mounting

Hi, one of my 6TB WD Blue backup drives will not mount. Formatted OS extended journaled. I tried switching out the ports, cables, dock, even tried on a different Mac. It shows up grayed out in disk utility. The mount command does nothing. I also tried to force mount via Terminal - followed a YouTube tutorial that helped others (https://www.youtube.com/watch?v=QMvYHgQOEvA). Disk first aid fails. Someone suggested Disk Warrior, but hate to spend $100+ when I read comments that it's no more powerful than OS repairs. Any advice is much appreciated. Thank you.