A limited-slip differential helps limit the difference in wheel speed between the driven wheels when traction is uneven. Depending on its design, it uses clutches, gears, or other mechanisms to help direct more usable torque to the wheel with better traction.
It still allows the wheels to turn at different speeds when cornering. It is different from a fully locking differential and cannot guarantee traction in every situation.
Fluid and additive requirements vary by differential design. Certified Transmission in Bellevue can help identify your vehicle's differential and the service requirements that apply to it.