OK, I found my file: E:\ArcGIS10.5\Lib\site-packages\Desktop10.5.pth and opened it to see:
E:\Desktop10.5\bin
E:\Desktop10.5\ArcPy
E:\Desktop10.5\ArcToolBox\Scripts
Exactly as the example said it should be. I double checked and the files are located in their respective locations - check.
However, then I went in and looked at the actual code for the Exploratory Regression tool... then I went in to a tool I know is working (Iso Cluster Unsupervised Classification) and I viewed the code.
I thought I might have stumbled upon the problem from my poking around when I realized that C++ is CASE SENSITIVE maybe the problem lay in the code as such:
IsoClusterUnsupervised.py is written all lowercase but without an import statement.
Whereas the Exploratory Regression code says: import arcpy as ARCPY
...
Now my file says E:\Desktop10.5\ArcPy so everything should be good right? Nope.
The ACTUAL file location is E:\Desktop10.5\arcpy
So I changed the pth file to reflect this change, I didn't think it would work - it is giving me line numbers for the errors right? so it must be making it to the files... I was right and it didn't work (always hopeful for the simple fix) but wanted to try SOMETHING.
Then I read this article Enable Python installations that were not installed by ArcGIS to access Arcpy functionality | Python... so ok, go to the system file and add the path there... still no good. I don't have another code to delete it all (including the past remnants that did not get removed when I did the uninstall of the prior version) and start again.
Any other ideas please I have to get my project done and at this point I may have to abandon Arc to do the analysis that I will then have to bring back into Arc - not ideal!