Here is usually the number 1 reason for a delta faucet to leak, no matter what faucet it is.
Seat cups and springs are the parts of a delta faucet that over time will wear down and need replacement. The parts are relatively inexpensive given the fact that the newer faucets all have pricey cartridges with no smaller parts to replace.
The most common mistake that property owners make is not replacing these components with OEM parts. (Original Equipment Manufacture)
Delta seat cups will be marked on the underside of the rubber cup, and they always look like they have a white glaze on the rubber finish. This is embedded silicone that helps prevent the friction that is notorious for premature wear over time. This mating surface combined with the chemicals commonly found in water contributes to the issues we find in plumbing that break down the moving parts.
