I have a MacBook Mid 2010 and an iMac 21.5 Late 2012 both OS 10.13.6. The Security Update 2019-006 10.13.6 installed without issue on the MacBook Mid 2010 first try downloaded from app store . The iMac 21.5 Late 2012 is troublesome: After the Security Update 2019-006 10.13.6 failed twice to install from app store, I downloaded it from the above link. [I started in Recover and installed new OS between the the app store downloads and the download from the above Link (https://support.apple.com/kb/DL2023?locale=en_CA)] I get a message "[MacOS could not be installed on your computer, couldn't mount disk Quit installer to restart your computer and try again"] after both app store downloads and downloading from the link above. Still would not install so I attempted to install in "safe mode" On restart for installation received the "MacOS could not........" I restored the iMac from Time Machine to the week before the first attempted install....As soon as I download and restart same message. I did notice during the install the "progress bar indicated full progression" and there appears to be no progress, then, after 4-5 minutes get a message "Restart to complete installation". I read on Apple Communities might try downloading and installing OS 10.13.6 Combo to and start with a FRESH OS. (https://support.apple.com/kb/DL1970?...K&locale=zh_HK)
I am hesitant to download it. Although the language tab indicates "english" some of the information appears to be in one of the "Oriental" languages.

I did uninstall all 3rd party applications and preferences from libraries after restore from Time Machine, SO, Could I be facing a erase and clean install? Any other input or suggestions welcome!

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