External disk is hijacked by fsck when plugged in to Macbook External disk (2 TB Seagate) is captured by fsck when plugged into a USB 3.0 port on my Macbook Pro (macOS Mojave 10.14.5). This has been discussed by @ArielAllon, and indeed, when I kill the fsck process, the disk is immediately mounted and I can see and read it. When I eject the disk and plug it in again, I always have to kill fsck. I have left fsck running for 12 hours and it never completes. When I kill it, a pop-up warns that the disk could not be repaired.  

My problem now, as Ariel mentioned, is that the disk is read-only, owned by root (or wheel?). I would like to use the remaining 150 GB on the disk, (remove old backups, etc) and prevent fsck from capturing it when attached. Thanks for any help...
The two items that come to mind are getting software that can try and repair the disk structure and prevent the mounting like Disk Warrior or connecting the drive using a USB write blocker / forensic adapter so that the disk just presents as read-only so you can get any data off it.

Then, you would wipe the drive if you can’t get it sorted. The native tool will choke on fsck even if you disable the automatic check when it comes time to mount the drive normally.