I've run a similar test on my own blog (links dating back to ~2000), and I had the same problem. Some sites do a permanent redirect on broken links, others don'

I've run a similar test on my own blog (links dating back to ~2000), and I had the same problem. Some sites do a permanent redirect on broken links, others don't even redirect but show generic content on the original URL. I guess your success in automating this would depend on the nature of the links, but from a completely random collection the only success I had was with visual inspection. (Someone with far too much time on their hands could probably write a script to attempt to retrieve a copy of the page from the Wayback Machine from around the time the link was posted, then calculate the percentage change compared to the current version. Not really reliable, but worth a try.)