3135 Slowing Down After a Decade

[No SUBctitute]

I have a 3135 sub that has averaged about +1.5 second per day for more than a decade. I hadn't checked the accuracy for a few years, but it now seems to be almost dead on. It has not been serviced.

Assuming that nothing more than normal wear and tear is happening to a movement (and it has not undergone anything traumatic), is it more usual for the 3135 to slow down or speed up over time? Or are either just as equally likely to happen?

To clarify, I am perfectly happy with my watch the way it is--I am not asking about my watch specifically. I was just curious as to how a 3135 usually behaves as it ages. Or if there is no "usual."