I was working on a house with 30 year old Leviton GFCI receptacles. Three would not trip when tested with a 6mA load. On two of them the test button did not click and did not trip the GFCI. On one GFCI the test button clicked and popped up the reset button, which could then be reset--but at no time was the power disconnected. A false test button test. All were installed correctly. Two were high usage, bath and exterior outlet, one was low usage. Do GFCIs have a replacement life?