I had to replace the hatch gasket on my newly acquired Current Designs Extreme / Nomad same kayak. Few tips the new gasket is sent in two pieces. There is the outer piece you see and it has a U shape that you press on the fiberglass flange. It is like a door seal on your car. The second piece is a 1/4" approx. diameter neoprene tube. It fits in the outer piece. Problem is getting the solid tube in the outside gasket. After looking at it and trying a few things I went with the following method. Took some mason line 176# test tied it tightly around the tube which I cut on a slight angle 45* then dropped the line through the outer gasket when hanging. Then I took some water and poured it through the tube followed with two pumps of Dawn soap. This makes it slippy enough to pull it through fairly easily. Then pull the solid tube past the outer gasket about 3-4". Both pieces are the same length after you measure what you need around the flange. You will have to cut the U shaped gasket with a fine hacksaw. May try to put pictures up later which I took. Other companies may use the same gasket.
like this http://www.austinkayak.com/products/1559/Trim-Loc-Hatch-Seal-Foot.html only solid tube goes full length.