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> My Canon waterproof camera came with a tube of silicon I had to dab on the battery compartment gasket

And those devices are MORE water resistant than most phones. The grease is to improve ingress protection beyond what's possible with double sided tapes used in "waterproof" phones. And the manuals for that gear should mention a retention period of x hours under y depth counting down from the moment the housing was closed.

Contrast to that, waterproof ratings for most glued-shut waterproof phones are invalid after purchase. Out of package, out of spec. Most manufacturers don't honor warranties for water damages for waterproof phone, and very few offer requisite gasket maintenance to retain waterproof ratings.

Apple doesn't have a recertification option even for battery replacement at Apple Store. Do ANY service and it's invalid. Not waterproof even in THEIR hands. Frankly their terms is one of the most egregious.