GMT Master Help Needed - Loses 1 Minute/Day

[Indierolex]

This sounds like the either cannon pinion may be beginning to slip or the hand itself is beginning to come loose. When the watch gives an accurate timing trace but the time displayed doesn't follow, one of these two problems is usually the cause.

The cannon pinion is fitted in such a way that the hands will move along with the movement but the connection can be interrupted for hand setting. Over time, frequent hand setting can cause the relationship between the hands and the movement to be too loose, so the hands will not advance correctly with the movement.

Cure is to tighten or replace the cannon pinion.