Do I need to buy a bulb separately?

Bulb is not included with this assembly. You'll need to source the correct bulb type for your model year — check your owner's manual or ask at checkout if you're unsure which one you need.

Will I need fasteners to mount this?

This uses the factory mounting points, so fasteners are already in place on your vehicle. If you're replacing an existing light, reuse what's already there.

What if it doesn't seal properly after install?

Test-fit first before final installation. If water intrusion occurs, verify the rubber gasket is seated correctly and all mounting bolts are snug. Replacement is straightforward — pull the old unit, swap in the new one, and verify the fit before driving.