The problem with any vintage underwater camera, as I recently found out, is the O-rings wear out. There are users serviceable O-rings, and there are O-rings deep inside the camera that require a pretty heavy disassembly to get to. Now, since these cameras are no longer made, finding the right replacement O-rings can be challenging, if not impossible. Add to that the fact that these cameras have likely spent a good bit of time in salt water, which is extremely corrosive, and you've got a recipe for a money pit that only leads to disaster. On top of all of that, using one is no easy task. The light changes with each meter you dive. The waves are pushing your around. It's hard to see out of your mask. Everything is moving around you, and you have to be ultra aware of your surroundings at all times, which makes operating a hard to use camera in your hands even more difficult.
So in all honesty, I would recommend a digital camera. Barring that, I'd recommend an underwater housing for a camera you're already familiar with (but one that's not too precious to you, because even under the best of circumstances, these things can spring a leak and flood your camera). Autofocus is really, really handy. Almost mandatory.
I recently went snorkeling in Hawaii and took two Sea and Sea Motormarine II cameras with me. Before I left, I replaced all of the old O-rings on one, and the other one looked to be in pretty good shape, so I left it as is, and used it as a backup. They were both watertight in my bathtub. I also brought an external flash to use with them, which I also replaced the O-rings on. Unfortunately, I couldn't find exact replacements for all of the O-rings anywhere online, so for a couple, I bought O-rings that with slightly larger diameters (in thickness, not in length) than the originals, thinking they'd compress to fit and work, if provide some extra resistance to knobs and such (this is what was recommended to me online). It didn't work. In my bathtub, they were fine. In the ocean with waves thrashing me about, both cameras flooded before I finished the first roll of film. The flash, however, held together and never gave me issues. Both cameras were destroyed by the corrosive effects of salt water, and so I threw the entire kit away into the hotel room's trash. It was disappointing, but at least I didn't spend Nikonos V money on them only to have the same results.
With a housing, you can see if it's starting to flood. That buys you enough time to maybe surface and save the camera. Also, you might be able to more easily find exact replacements for the O-rings. And, an autofocus, autoexposure camera not only makes things easier, it makes things much safer. I was constantly dodging rocks (cause that's where the fish and sea turtles where), other snorkelers, having to keep my head on a swivel, all while trying to zone focus on animals moving one direction, while I was moving the next. I developed two half rolls from that trip. I got zero good shots, and only a handful of shots with a useable exposure where the subjects were modestly in focus. Next time, I'm renting a digital camera. This is one of those areas where digital is hands down the better choice in every conceivable way. I wanted film to work. But it's just not a good idea. And a good digital setup is very, very expensive. So unless you're wanting to make a living off this, I'd also recommend renting, or buying a cheap, water-safe P&S. A Nikonos would still be a good camera for shooting in the rain or under the surface of streams, in swimming pools, and such. But I can't recommend one in today's world for snorkeling or diving.