How can I independently verify a Rolex Submariner’s authenticity and seaworthiness?

Hi — I’m Pedro. I’m skeptical and need concrete, testable checks before trusting a used Submariner. Looking for concise technical steps I can do myself or with a local watchmaker: 1) External checks without opening the case: which dial/rehaut/bezel/cyclops/font/lume details are most reliable for spotting fakes? 2) Timegrapher readings: what amplitude/beat error/positional variance should I expect for an authentic movement (3135/3235) and what values are red flags? 3) Water resistance: can a reputable independent watchmaker safely pressure-test to 30 bar, and how trustworthy are dry vs wet tests compared to an official Rolex service? 4) How to detect aftermarket parts or refinished dials/hands with a loupe or common tools? 5) If paper/box is missing, what documentation or provenance is actually useful? Keep it practical and technical — I won’t trust vague answers.