Hi Stewart,
Thanks for reporting this problem. The issue was caused by the fact that we installed Subversion from a newer Debian version than the Debian version we're using for the base OS. However, that newer version didn't have a ViewVC version anymore due to lack of Python2 support.
The ViewVC repository *does* have Python3 support. It was enough to run ViewVC from git (no version with Python3 support was released yet).
In summary: we've resolved the situation; no need to update your links!
Regards,
Erik.