Mail, Contacts & Calendars refuses to connect to Google

Since yesterday the System Preferences pane on Mail, Contacts & Calendars refuses to connect to Google to setup e-mail, calendars and contacts. It started after Contacts.app did not want to sync with Google Contacts and asked and refused my correct password. After that Mail.app and Calendar.app did the same. I removed the account from System Preferences and attempted to start anew.

However, now it throws the following error at me:

Nowhere in any log I know can I find more information on the error. When I monitor the connection using Little Snitch it shows that the following connections are attempted:

I can ping them all through Terminal.app successfully.

I have no 2-step verification, so I'm not using application specific passwords in Google.

This is what I've tried, all without a positive outcome:

• Add a Gmail account in the Guest user (same error).
• Make a new Gmail account, try to add it (same error).
• Enable 2-step verification, make application specific passwords (same error).
• Run Keychain first aid.
• Verify & Repair permissions.
• Verify & Repair disk (volume bitmap needed minor repair for orphaned blocks). After repair still the same situation.
• Reverted /etc/hosts file to default.
• Disabled Little Snitch.
• Boot from external drive into Yosemite, try to add the Google account.
• Try connection through ethernet instead of airport express.
• Try connection through a different network entirely.
• Following the troubleshooting steps from Google.
• Allowing "less secure application" (that still use OAuth 1.0) to login to Google.
• Resetting the Keychain

I've really exhausted my Google-fu and little knowledge I have on Macs. I would really appreciate some pointers on where to look further.