Rolex GMT-Master is an accurate timepiece. The company standard is +2/-2 seconds per day. It means that your Rolex GMT-Master should not gain or lose more than 2 seconds per day.
There are several reasons why a Rolex GMT-Master is no longer accurate, including but not limited to:
1. Rolex GMT-Master suffered a high impact
If the Rolex GMT-Master has been dropped on the floor or suffers a significant impact, the watch movement could be affected. Rolex GMT-Master is not an electronic quartz movement; it's a mechanical watch with many delicate parts:
- the mainspring, which powers the watch
- the balance wheel and hairspring, which oscillate to measure the time
- the escapement, which allocates the oscillator pulses
- the gear train, which transfers the power
- the dial train, which moves the hands
- and more
Each element is precisely positioned on the calibre to make the watch accurate. Rolex movement is robust, but a violent impact can displace one or more elements. After an impact, a loss of accuracy is an indication that the watch movement has been damage.
After an impact, it a good idea to test the Rolex GMT-Master accuracy for 48 hours. If the time remains accurate, it will be good to know that the impact has not affected the Rolex GMT-Master. However, if the watch is losing more than 2 seconds every 24 hours, the impact has affected the watch. How seriously? Is it difficult to know, but the watch needs to be examined at a Rolex Service Centre.
2. Watches low on lubricants
The Rolex GMT-Master needs lubricants to remain accurate and to reduce friction between the various moving parts. The term 'running dry' is used by watchmakers to indicate that the watch's lubricant level is too low.
Typically, Rolex lubricants last between five years and ten years, but that is a general timeframe. Is it ten years from the time of purchase or ten years from the time the watch was manufactured? How long between the time of manufacturing and the time you purchased the watch? There are some unknowns about the actual lifespan of lubricants.
Rolex uses a specific lubricant that evaporates when drying. When the lubricants are low; they need to be replenished. The operation is carried out by a qualified watchmaker who knows precisely the type of lubricant to use, where and how much needs to be applied.
A symptom of lubricant running low is the Rolex GMT-Master losing few seconds per day. A Rolex GMT-Master running fine should not lose more than 2 seconds per day. If the watch is losing, say 15 seconds per day, that is no normal. A possible explanation is a lack of lubricant. If it the case, the problem is not only that the Rolex GMT-Master is not keeping time. Low lubrification will increase the wear and tear of the movement. The added friction will worn-out the gears inside.
Testing your Rolex GMT-Master accuracy is an excellent way to check that everything is ok with your watch.
3. Watches Water Damage Aftermath
Water damage can cause a Rolex GMT-Master to run slowly. Dirt, sand, and minerals are left inside Rolex GMT-Masters by water or condensation. If water has penetrated your Rolex GMT-Master, you need to take it to a Rolex Service Center right away. The movement of a Rolex GMT-Master is susceptible to damage from any type of water, but saltwater is most dangerous.
The Rolex GMT-Master needs repair immediately, no matter what the cause. Rolex GMT-Master watch repairs will become more expensive if internal damage is not addressed in a timely manner.
The Rolex GMT-Master still has moisture and deposits inside, which will slowly damage the movement. When a Rolex GMT-Master runs slow, it may be an indication that the movement has deteriorated. The worst case would be rusting. Rolex watchmakers are the only ones qualified to mend a Rolex watch that has suffered a water leak.
You are probably aware that Rolex GMT-Master if has been water damaged. Testing its accuracy isn't necessary. I would recommend that you send the watch in as soon as possible for service.