I have had a couple of problems with 42.3. One was with installing, not being able to get a single forward slash / for a mount point. I seem to have overcome the latter problem by deleting the single partition that I wanted to install to and leaving it unformatted until I start the installation process. It was still quite finicky and i found myself having to edit my options with expert partitioner before I had the option to mount to the root / of that partition. The other problem that persists is that 42.3 seems to want to write the MBR to sdc instead of sda. I now have to use the BIOS to enter the OpenSuse generated boot menu on my 320gb disk sdc which is the one with all my Linux partitions on it. It works but I would like to be able to edit it and change the order of the items and remove the many advanced boot options. It is very slow and jerky and at least once when I entered my Windows menu from this boot menu I was not able to get into my PIN box to login to Windows 10. Is there a way to improve the 42.3 generated boot menu generated on sdc or to customize it. Alternatively is there a way to add OpenSuse to my grub2 boot menu on sda so I can boot from the original grub2 menu? I was looking but could not find any way to force 42.3 to write Grub to SDA instead of SDC
I assume that all booting of all OS are MBR and none using EFI boot mixing boot modes is bad. You can set what drive boots in the BIOS/UEFI. You may have to re run osprober to add the new OS to an old grub menu. Can be done in Yast-bootloader or the command line if not running openSUSE
You description of what you did and what went wrong is very much unclear. When installing just give the installer free unpartitioned space to use. Otherwise you must take control and setup exactly what you want the installer is not good at reading minds. 
Thanks for your reply. Sorry that my explanation was not clear. Part of the problem is that I didn’t see all that I needed to see regarding setting boot parameters. The other problem is that I forgot most of it. I could have used software or videocamera to recorded what I did. Could you please spell out for me how to “re run osprober” to add the new OS OpenSuse 42.3 to my old grub menu on /dev/sda/. I don’t have OpenSuse when I boot from this hard drive so the option would be to use the command line in terminal. Alernatively what would i do inside Yast2 if I change the boot drive in BIOS and boot to OpenSuse from /sdc and tried to move the grub information to sda. I have since update and/or reinstalled most of the Linux OS’s currently booting from sda. None of the os probers saw OpenSuse on /sdc or added it to grub.
I tried using Yast in OpenSuse 42.3. After around 5 minutes of hanging on “saving configuration.” an error box popped up saying “execution of command [/usr/sbin/grub2-install,”-target=i386–pc", “force”, “–skip-fs-probe,”/dev/ada"]]" failed.Exit code: 1 /usr/sbin/grub2-install: warning: your core.img is unusually large . It won’t fit in the embedding area. /usr/sbin/grub2-install: error filesystem ‘btrfs’ doesn’t support blocklists, Would anyone care to translate this?
It my be that the other Linuxes don’t support BTRFS Also if you mix boot modes ie some using MBR and some EFI they won’t see each other. All OS must use the same boot method!
I have never seen any reference to EFI (is this UEFI?) before in Windows 10 or in my BIOS settings.
UEFI is the modern replacement for the old BIOS (basic input output system). EFI is the preferred boot method of UEFI system , but you can chose legacy boot which is the old MBR boot method. If unsure show use the output of fdisk -l and we can see what you have. If all other OS are MBR boot then it is possible if this machine is less then 6 years old that you accidentally chose to install openSUSE in EFI mode rather then legacy and thus one OS will not see the others and visa versa.
Thank you for this information. My Asus P5B-VM was manufactured in 2007 afaik. I picked up a core 2 quad p6700 cpu on ebay 4 or 5 years ago which made a huge difference in the speed over the orginal P4. I flashed the latest BIOS revision to enable the Core 2 quad to work. Do you think there is anything I can do now to make my Opensuse bootable from sda?
So MBR boot with BIOS
Show fdisk -l please
Also exactly what are the other Linux installs.
Some Linux may not support BTRFS thus they can not boot or see what is on the openSUSE. Might try using ext4 instead
You do not have enough space to install bootloader in MBR. You should configure YaST to put botloader in partition (root or boot, depending on your partitions layout) and place generic boot code in MBR. To say more you need to provide at least “fdisk -l” output.
This says your bootloader will not fit where you are trying to install it (the MBR). You need to choose to write generic boot code to the MBR and install the bootloader to the /root partition.
Edit: Oh. I see arvidjaar already gave you the answer.