Ah! I have found one file with whitespace outside a tag!
Now fixed and testing …
FIXED 
Here was the problem. It was in a file that we had added “classes/invoice/Invoice.inc.php”
It had extra blank lines at the end.
This was not picked up in my script as it did not exist in the original OCS 2.3.6 code and so my script didn’t do a diff of it against existing code.
I will check other files but it looks fixed for the one Word doc I checked.
Your help is so much appreciated