My Oris Williams F1 Day Date has a power reserve of only 31 hours after fully winding and leaving it dial up. I've owned it from new since 2010 and it was serviced several months ago. The movement is an Oris 635, base ETA 2836-2 which is supposed to be good for 38 hours and all my other watches manage a few hours over their spec power reserve.
My watch guy has had a look at it a few times and says he can't see anything wrong with the movement or the power reserve. Anyone have an idea of what the problem might be and how it could be fixed? I'm thinking perhaps there is a problem with the barrel or spring. Is it normal for watches to lose their power reserve over time?
Thanks in advance.