One of the few things that can render a Rolex movement beyond repair is moisture. Unlike electronic devices, moisture damage in mechanical watches is not caused by the instantaneous presence of a conducting liquid. Rather, the damage results from the rust and corrosion that takes place after the movement has been exposed to a liquid.
Most contemporary watches have cases made from highly corrosion-resistant materials; however their delicate movements inside do not share this quality. Even a small amount of moisture inside a watch case can cause significant levels of corrosion if left unattended. Corrosion can quickly spread from one piece of the movement to another, and the longer it is left to sit, the worse the corrosion will become.
Some of the most extensive (and expensive) Rolex repair jobs are cases in which moisture has entered the watch, and it has been left to sit for an extended period of time. Even in instances in which a significant amount of water has entered the watch case, the vast majority of parts can be salvaged if the issue is addressed quickly.
Due to corrosion’s ability to spread and worsen, it is best to send your Rolex in for servicing as soon as possible, should you notice moisture inside the watch case.