I am a brand new member of the forum and hope I'm following protocol in asking this here. After a seamaster or constellation from the 59s or 60s is serviced, is it water resistant or "waterproof"?

 

After that it is "away-from-water-as-possible-proof"
Even after a good service, for vintage watches it is difficult to restore a perfect sealing (without changing almost all the case!!)

 

Could be yes, could be no - depends on the specific watch. Some can be made to be water resistant again if the case is in good condition, and all the seals are replaced. Some even replacing all the seals won't help, because the case is either corroded, deformed in some way, or has some other problem, that keeps it from being water resistant.

The only way to know is to have the watch pressure tested. Then decide based on the results if it is something you want to risk - water resistance (if it is present at all) is not permanent and must be maintained over time.

Cheers, Al