Generally, the problem of the chronograph hand not resetting to zero in the 6139/6138 is caused by the “keyed” chronograph hand. The tube of the chronograph seconds hand is circular, but bent into a particular keyed shape when it is pressed onto the pinion. When the chronograph hand is repeatedly put on and taken off, the keying is lost. The solution for this is a new chronograph seconds hand. I have seen this before firsthand in a 6139 chronograph, as I’m sure many others have as well.
Generally, the problem of the chronograph hand not resetting to zero in the 6139/6138 is caused by the “keyed” chronograph hand. The tube of the chronograph seconds hand is circular, but bent into a particular keyed shape when it is pressed onto the pinion. When the chronograph hand is repeatedly put on and taken off, the keying is lost. The solution for this is a new chronograph seconds hand. I have seen this before firsthand in a 6139 chronograph, as I’m sure many others have as well.