Some progress (but not quite there yet)
The failed install is a Node 12 vs Node 10 issue
If you install Node-RED that doesn't have a supported version of node - it will install the latest stable version. (which since 26th Nov 2019 is 12.13. 1)
My normal working Pi4 Node-RED was installed back in August and is running 10.17.0
On my new image, I used this to install n and roll back to 10.17.0 and node-red-contrib-i2c installed this time
However, it doesn't seem to actually work so more investigation needed
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