Here's another method: Get the white liquid glue that kids use for collage etc that sets with a rubbery kind of consistency.
Apply it to the grooves and let it dry overnight, taking care not to get any on the label. Peel it off carefully the next day. NB: I haven't used this method, but a beat digging friend has, he reserves it for those ultra rare pieces that are frustratingly f**ked up since it's somewhat labour intensive. Obviously won't get rid of scrathces, but will remove really deep dirt. I'd recommend trying it on a low value record first!
