From memory they still have a seal in there regardless though if the watch hasn’t had the seals changed in a while it might not be any good at keeping water out
You should be fine. Assuming the He valve on my planet ocean is similar the watch is still water resistant to 50m with the valve unscrewed. Just rinse the saltwater off after the swim.
To quote from page 34 of the Omega Operating Instructions book that accompanied my 2255.80, "Even if the valve is unscrewed, the watch is still water resistant to 50 metres"
Rinse with clean water, let it dry and all should be well.
I knew it was water proof... surprised it is only to 50m. You have to admit Rolex gets a bit of a nod on this one.
For the record my POC manual makes no reference to the ability to use the Chrono pushers underwater.
Your's may well be an updated version of my Omega Operating Instructions book, but on page 4 mine says:
"Chronograph push-pieces: do not operate chronograph pushers under water in order to prevent water entering the mechanism.
Exception: the Seamaster 300 m Chronographs have pushers which can function under water."
Now, to preserve my blokiness, I'm putting the instructions back in the box and promise never to look at them again 😁
