> Also I'm probably forgetting something so you probably actually have four options.

I looked into this some more and there is a forth option! A dripless shaft seal (there are different names for this as well) uses a collar that rotates with the prop shaft and a graphite or carbon stator that presses against the collar. The graphite stator is self lubricating (seawater works as a lubricant as well) so its supposed to require very little maintenance. Here's an article that explains it pretty well: https://www.passagemaker.com/technical/troubleshooter-unders...