Skip the pre-fab or bulk kits. They're absurdly over-priced for some popsicle stix, handholding, and a bit of foam. Nearly all MF Nikon SLR leaks trace back to the hinge side of the back--simply take a look and you'll likely see the problem. No need to fuss with the long channels the back fits into--they're baffled without foam.Use some thin adhesive-backed felt or foam from a craft store. A straight edge, an Xacto or single-edge razor blade and some patience will produce what you need. Lots of online how-to diagrams for cleaning out old gicky foam.