This was the most trying update I have done in recent memory. First attempt ultimately failed with error 0xc0000374, after about 3 partial installations and 3 GTR bounce backs. After deleting the contents of C:\Windows\SoftwareDistribution\Download and
restarting, the second attempt completed, but not without a partial installation to 25%, GTR bounce back, then a complete installation. Up and running build 18932.1000...hope it proves to have been worth the effort.