You should avoid using standard WD-40 on a shower diverter valve. While classic WD-40 is a water-displacing solvent that temporarily frees stuck parts, it is a petroleum-based product that rapidly washes away and degrades rubber O-rings, plastic seals, and washers, eventually causing worse sticking and leaks. Instead, always use a food-grade silicone grease (plumber's grease) to lubricate plumbing parts safely. Verification: Pull and push the diverter knob after greasing to confirm smooth, lubricated movement.
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