Unfortunately, CM, blue, and seven are probably right. This is a serious problem because the resulting overheating can do damage as can coolant in the cylinders. Before you really tear into things you might want to use a coolant system pressure tester (usually a free loaner from car parts places) to verify that you really have a leak. You can also pin down the specific leak by listening at the intake, exhaust, and crankcase for the sound of air leaking from the cooling loop. Best to drain some coolant for this test.
Assuming the head gasket is leaking, recommend you have head checked for flatness at a machine shop before reinstall. If the head is warped, the new gasket will leak eventually. A good machine shop can "plane" the head to remove any warp and it's not that costly.
I don't have a DK55 book and I didn't see head bolt specs in the DK50 book (some bolts are spec'ed by max length or min diameter). So if in doubt, replace.