The wet spot on your ceiling is the end of a path. Rain can enter farther up the slope, follow the roof deck or framing and appear in a different room. Sealing the spot above the stain without tracing that path can leave the actual opening untouched.
A roofer checks the covering and the nearby details together. A split plumbing-vent collar, a lifted shingle or flashing that no longer overlaps correctly can each admit water. The repair has to restore the way those parts shed rain, with sound material underneath and around the work.
That is why a leak does not automatically mean replacement. The question is how far the problem extends once its cause is understood.
Start with a free inspection