Leaks are in tubes, not tires. Patch or replace the tube, and your leak will be gone. Your tire may or may not be worthy of replacement, but not because of a leak. Even if a puncture leaves a visible rip in the tire, the rip won't leak air, because the tube is the air seal. Old tires are vulnerable to punctures and sudden ruptures, but they don't leak, since, as I said, the tube is the air seal.