Barrel mainspring 'slipping'

[Overbias]

Hi all!

Had my GMT back for a couple of months after extensive service. It was keeping great time until about a week ago. Has been gaining almost a minute a day. So I took it back to the watchmaker who took it back in after testing it.

The explanation he gave me was that the mainspring, which should normally slip insight the barrel, to prevent overwinding, was getting stuck effecting the mainspring tension. This was in turn causing the increase in rate.

Does this sound plausible? He is replacing the barrel and I am picking up tomorrow. Super quick turnaround so great service. Just wondered what the collective wisdom here has to offer on the explanation?

[Andad]

An interesting explanation.

Let's see how it runs when you get it back.