Watch with caliber RONDA 515 damaged. Let's find out what happened

Forensic watchmaking.
A relative brought me a RONDA 515 caliber watch that intrigued me. He assured that it did not get wet, no battery leaked inside it and it did not receive blows, but suddenly it stopped working correctly. Due to the symptoms, the clutch seemed worn, but it did not fit me with a caliber of the quality of the RONDA, with only 15 years and more knowing that that person turns the hands little and carefully. So not only was I interested in repairing the watch (he couldn't say no to such a close relative), above all I was interested in knowing the reason for the failure.