I don't own a ronstan but I wore my breitling chronomat out sailing. When using the buttons salt water intruded into the watch and destroyed the watch. Even though the watch was supposed to be good to 150 meters depth. I now have a $20,000 dollar boat anchor.
I don't recommend taking it apart yourself, take it to an authorized repair facility.
You wore a $20,000 out sailing?
A Ronstan Clear Start is ~ $100 and all electronic, so there's not much that a repair shop could do that wouldn't cost more than the watch in the first place.
The first thing I would do is replace the battery. These watches get flaky when the battery gets low. If that doesn't work, contact Ronstan and see if they'll warrantee it. firstname.lastname@example.org
If Ronstan won't cover it, the watch is more than likely toast, so there's no real harm in pulling apart to see if you can figure out what's wrong. It may be something simple that you can fix - like a loose contact. Meanwhile, order a new one. I'm on my fourth one, but I haven't had the buttons go bad - the strap breaks and they don't float.