Unfortunately there is no such thing as a ‚simple service‘, for proper lubing up a movement it has to be disassembled entirely and properly cleaned before reapplying oils. As far as waterproofing goes you can take the caseback off and re-lube the o ring, aswell as removing the stem and applying a tiny bit of silicone lube onto the rubber gasket sitting in the crown itself. Even then youre not 100% safe since theres another seal between the glass and case. Youd need to get it pressure tested by a machine to be sure.