If it is from the Metal Cap, and is 3 years old, I would replace it. Dealer; or Store will have them, but I found it a bit difficult to find in many stores. Our caps are infamous for leaking. Bend the Metal Tabs just a little bit to make for a tighter fit. Do not use a Cap with a Spring Loaded Center, as our Radiator and Overflow Bottles are all part of the Pressurized system. The Plastic Cap on the Plastic overflow Bottle is the Pressure Relief.