I was checking out some stats for my website with Google’s Webmaster Tools, and what did I see?
Google moved https://www.google.com/webmasters/tools/diagnostic to https://www.google.com/webmasters/tools/diagnostics (notice the trailing “s”) without setting up any sort of redirect. Google: how are search engines going to find you if you don’t set up proper redirects??
Not only that – but are you telling me Google can’t come up with a more useful 404 page?