How to find an old post using the old post number

I am no programmer. But in my simple-minded thinking, all it needs are a few lines of script. First, detect the old link syntax, then, redirect it to the post with the "new, improved" link syntax. It should be fairly simple. Right?

I've heard several times that all the search problems would be fixed but it seems they haven't been. I've had zero luck pulling up my favorite old posts.