Through the Viewfinder

I've been playing around with the TtV technique using a Kodak Duaflex. As you can see the viewfinder is rather dirty. I'm not sure whether to take it apart and clean it, as I don't want to get rid of all the imperfections... Has anyone used this technique and can give some pointers? Tell you what, it's so confusing trying to get the composition straight, as it's all a mirror image...

I've seen some really beautiful images done this way, and I love the old feel to them and the way it frames them.