Install Mint first, leaving sufficient room for Leap. Then install Leap. It’s GRUB configuration will automatically pick up Mint and list it in the boot menu.
Success!! But there is bad news with the good. The good side is that I did a new install on the second computer. This time, knowing that I would be using both Mint and OS, I created 2 partitions - one called Leap and one called Mint. Since I am starting to like OS over Mint, I decided to install OS Leap first. When it came to the disk config, I chose to use the Leap partition, and additionally specified that the root partition was to be EXT4. Leap installed okay and runs great. Then I installed Mint, and when it got down to disk, it already knew that Leap was installed and asked me if I wanted to install Mint along side Leap. Took that option (which disabled the option to use LVM with Mint) and Mint installed okay. Rebooted and grub comes up with options to chose either OS or Mint - perfect! I screwed up previously by installing Mint with the “use entire disk” option. I was unable to resize the Mint partition after the install - the LVM kept showing 100% used so could not be reduced by any partition tool. So cloned original disk and installed leap in the extra space but it didn’t know that Mint was already installed so I ended up with a one or the other scenario.
On the bad side, I followed JanMussche suggestions re the bios and ended up with a dead computer. Essentially it appears that the original owner also enabled stringent security on the box so if you mess with the cmos it renders the box unusable - all you get it 6 led flashes indicating bios cannot be authenticated. Losing a seven year old spare laptop was not a big deal but I hate when I do something that destroys hardware. So to JanMussche and others with bios password problems, be very careful before you try this solution!!
I honestly don’t under you messing around with LVM. It can get complicated and you should fully understand what it is and does before blindly using it.
Always read the hardware docs before messing with internals especially on laptops. removing power completely including cmos battery should reset to factory default. On some systems there may be a jumper set to take thing back to factory. If the cmos has not completely bled off then it is in a undetermined state. perhaps leaving all power unhooked for a couple of days