[ubuntu] Repairing grub partition??

A few months ago, I added a new hard drive to my system, installed Ubuntu on it, and set it up for multi-booting. My system had two other HDDs with Windows on them, and I followed the instructions for installing Ubuntu on the new (3rd) HDD, and for using GRUB to control which OS booted. This setup worked beautifully until yesterday, and the wheels came off completely!! Here's what happened:

1. While it was working (since Oct 2015), GRUB would prompt me for which OS to boot: Windows or Ubuntu
2. Yesterday, after retuing from extended travel, I booted into Windows (from GRUB), and first order of business was to get caught up on my updates.
3. Applied several Windows updates... then after restarting, the system began misbehaving: No GRUB menu appeared, and Windows automatically booted.
4. I booted from the Ubuntu install CD, and ran 'boot-repair' iaw some instructions I found on the Inteet, but this did not repair the issue:

a. 'boot-repair' reported that it could not fix the problem, and had me create a pastebin (??) URL:
b. paste.ubuntu.com/16674898

Further research yielded nothing useful - at least not pertinent to my situation as far as I could tell.

Any advice as to how to recover would be appreciated. I caot imagine how or why the GRUB partition became corrupted, but it seemed to happen as a result of applying updates to the Windows install (on another HDD in my system).

Best Regards,
JM