If the bearing you received is also an NTN bearing you could remove a seal from the used one and install on the new bearing. Use a very small flat blade screw driver to lift the seal from the groove it sits in. As mentioned above RS is a designation for rubber seal and I think LU is also an NTN designation for the type of seal they use. You may need to specify 6203 2LU or 6203 2RS when ordering.
Found this info below from NTN. This leads me to believe you may need to order a 6203LLU to get two seals. You want to stay with the LU seal to keep the water out.
•What is the difference between LLB & LLU seals? The "LB" seal is a non-contact seal for reduced torque or higher speed requirements. The "LU" seal is contact seal for better grease contamination control, but the contact friction increases torque and lowers the limiting speed.
