Two key elements to my SOLUTION were installing the 5.2.8 VB Extensions (after I got it to open my Win10 VM) and getting past my hesitancy to update the Kernel to 4.13.0-37-generic. Update manager had been nagging me to do so even before I switched from 18.3 with Cinnamon to 18.3 with MATE. That hesitancy was due to the suggestion to NOT update anything categorized as Level 4 or 5. Of course since I eventually installed VB via a download .deb file from Oracleś website, I´m ahead of the repository version.
After installing Mint 18.3 with MATE to replace Mint 18.3 with Cinnamon I installed repository version of Oracle VB. Immediately got update message when I started VB (recommended version 5.2.

Having had trouble when I installed a slightly older version under my Cinnamon installation I knew I had to get rid of all traces of the old installation, i.e. the version I installed from the repositiory. I believe it was version 5.0.#. command line options to remove/purge VirtualBox I did a search for ¨VirtualBox¨ under my File system. I deleted everything except the VirtualBox Machines folder in my /home. I don´t want to reinstall the repo version as it wouldn´t open my Win10 virtual machine. I´ve seen so many conflicting opinions about how to get VirtualBox 5.2.8 installed in Linux Mint 18.3 that Iḿ hoping someone in the Mint Forums can set my on the right path.
First decision is which version should I try? My system is 64bit, and I´ve read (on an Ubuntu forum) that Mint 18.3 is based on Ubuntu 16.04 so does that mean I should TRY to install that version of VB?
I downloaded the .deb but couldn´s get the installation to start.
Ubuntu 18.04 ("Bionic") AMD64
Ubuntu 17.04 ("Zesty") / 17.10 ("Artful") i386 | AMD64
Ubuntu 16.10 ("Yakkety") i386 | AMD64
Ubuntu 16.04 ("Xenial") i386 | AMD64
krustybaguette