Do the handlebars turn smoothly? If not, the cause could be corrosion in the bearing races. This picture shows what happens when a headset loses its protective grease, and grit and water take over. Rust and abrasion from dust and dirt will etch the bearing race.

New bearings are inexpensive and easy to install. Removing and replacing the bearing race is another story.

Another reason to maintain a bike. Grease well, grease often, ride forever.