Inspect The Rubber Seal - Optimum Time OS3 Quick Start Manual

9. Prior to replacing the back case inspect the rubber seal ensuring the seal sits
comfortably in its groove with no cracks or signs of perishing and replace if
necessary. If you need, or wish, to replace the rubber seal put some silicone
gel on your fingers and pull the new rubber seal through your fingers,
ensuring the seal is lightly coated. Carefully replace the rubber seal in its
groove with the tweezers, ensuring it's correctly fitted in its groove.
10. Replace the back case ensuring the cover is aligned appropriately. Ensure
that the 'TOP' marked on the back aligns with the Stop / Start button on the
front.
11. Carefully replace the screws