So, first is to confirm the case ref by removing the back. If it is 535.(0)011 then that crystal above is shown for it and it has the yellow tension ring for a gold coloured case.
You can remove the back with one of those balls or similar items unless it is on really tight and then you'll need your watchmaker. Just fitting these tension ring crystals is not that easy so, I would not recommend trying that unless you've done it before.
If it is running fine, then it's up to you whether you decide to service it but, running fine is no indication of the state of the movement. I'm sure you know that.
The problem is that the oil oil, dirt and dust combine to make a very efficient grinding paste and will just wear the pivots out as well as other parts. All that means is when it does eventually get serviced, you may be looking at parts, which are not cheap. Like I say, up to you.
To show what I mean, here is a centre wheel on a cal 351 that I have just completed. The one on the left is new and the one on the right is the original. You can see the pivot is grooved and ruined.
View attachment 432920
I suspect that the box, buckle etc will only be available from eBay. Can't help with those, sorry.
Here's one of the watches I did for my wife, some years ago (in the middle, obviously), and it's one of her favourites. Tiny 684 automatic in it. Bit different to her dress watches.
View attachment 432922
Good luck, Chris
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