Greg
For the second time today I've deleted the tumbleweed repo from zypper and re-added it via:
sudo zypper ar http://download.opensuse.org/repositories/openSUSE:/Tumbleweed/standard/open...
This time is seems to have really worked and suddenly I'm seeing packages in the Tumbleweed repo.
I have no idea why it wasn't working a few hours ago, nor why it did work this time.
Maybe the repo file itself was still mirroring out some key info.
Sorry for the noise, Greg