Aqua Terra 8500 issue

So my wife's aqua terra has started to stop intermittently. Today it stoped for about 2 hours before she noticed it. She pulled the crown out to wind and it started up again. Crown was then screwed down. I noticed when she got home that her watch was about 4 minutes ahead
of mine (strange because all of our 8500 cal movements run pretty spot on with each other).

Tonight I decided to fiddle with it a bit. Pulled crown out to position 3 and gave it a spin. Only to find that the crown fell off into my hands 😲

I've never had this happen to any of my watched. Especially the 8500 cal. We are the second owner of this watch and the previous owner wore
It everyday and it shows.

We have the first iteration of the 2nd gen aqua terra, reference #231.10.39.21.02.001

I'm guessing it's time for a service. Just wanted to consult with everyone and make sure it's not just a crown stem that needs replacing.

Thanks
Adam

Thanks @Archer, this is kinda what I was thinking.

That's good to know. Do you happen to know if Omega replaces the existing barrels with the newer barrels from the 8508/8900 movement when the watch is serviced. I was looking through some old threads on this and you mentioned something to this effect but I wasn't sure. Thanks.
Adam

Got it. Thanks. There is no way this has an 8500G movement, its way too old.