Check the retainer plastic ring that holds the tank onto the pump. Lipart repaired my pump out of warranty because the ring had cracked. The replacement ring was twice the size of the original. the tank is only secured to the pump by the ring. I suspect that the weight of The full tank and road vibration could of caused the leak over time and the ring was not stout enough to withstand the vibration. The other thing I saw posts on was about the O-ring. Any mark on the O-ring will eventually cause a leak. The repair was make 5-6 years ago, no problems since.