Twice I noticed that the watch has lost approximately 3-5 mins randomly. Could this be : Not fully charged/ wound Problem with movement ? Or simply does the watch slow down before stopping ?
I have the same issue with my 300M. Different movement than yours, I realize. Mine runs like a Swiss watch for weeks then looses 3-5 minutes in a day, while still fully wound. Tried all positions, wearing it, leaving it on the winder set at 900 RPM. Nothing seems to make a difference. It's been about five years since the last service, so I'll be bringing it in to the local OB for a full service.