Gardena Aquazoom 3900 started sticking at one end of the oscillating cycle

An oscillating sprinkler is placed on the ground and fans out horizontally from one side of the sprinkler base to the other. The features an adjustment knob located on the base. The sprinkler then oscillates up and down within the set rotation range. An oscillating sprinkler can usually be set to water just one area or to a full 180-degree range at different strengths.
You can use the know to adjust its settings.-------

Unscrew the faucet knob for the line or garden hose connected to the sprinkler. Verify the water is reaching the sprinkler and there are no kinks or bends in the line.

Shut off the water at the faucet and disconnect the line from the sprinkler to bleed any air trapped in the hose. This could cause the sprinkler to sputter and operate erratically.

Twist the screw in the oscillating sprinkler arm clockwise with a screwdriver to lower the arc of water spraying on a sprinkler. To cover a larger area, turn the screw counterclockwise.

Apply a short burst of spray lubricant to each end of the sprinkler arm if the unit does not oscillate. Wipe down the sprinkler with a rag. Corrosion, rust and grime may interfere with the sprinkler's normal operation. Lubricant loosens the parts so the sprinkler will oscillate.