This video show one possible reason for dripping faucet. In this case, the dripping is induced by the corrosion of the cartridge's bottom sealing metal surface. Due to corrosion induced by water over time, the cartridge's bottom sealing metal surface becomes very rough and even there appear some trenches, which leads to bad sealing and thus dripping from the faucet. In this case, the dripping faucet issue can be fixed by polishing the sealing surface. If you are working on a same or similar type of faucet handle valve, you may find this video helpful.