To help this seal up properly on the reassembly:
1. Don't use a metal scraper on the gasket surfaces when removing the old gaskets.
2. Remove all traces of the old gasket using something like this:
http://www.harborfreight.com/air-ang...der-32046.html
and this:
http://www.harborfreight.com/2-in-3-...kit-61561.html
BE CAREFUL! Do not round over the edges. Use a light touch!
3. Once everything is clean, put down a couple sheets of 400 wet-or-dry on a flat surface (table saw bed for example... must be FLAT!)
4. Use a black Sharpie on the gasket surface of the case halves, spray the wet-or-dry with WD-40, and then put the case half on the wet or dry and carefully (slowly) work the case making sure to hit all the areas evenly.
5. Inspect the surface often. Once all the black sharpie marker is gone everywhere, you are left with nice even gasket surfaces and are good to go.
The point of the above isn't to remove any significant amount of material. It is mainly to take out any local imperfections (dings, nicks, etc). You can start with a fine jewelers file first, but I like to finish up with the sharpie wet-or-dry sanding just to make sure everything is nice and flat.
Also remember: Do not use sealant on those gaskets. The factory didn't, and if you clean the surfaces properly you won't need it.