I saw that lathe the other day (looking for some other stuff). Just passed by thinking -- "do I have any place to put this?" The answer was "no" and I didn't stop to inspect it. But, it didn't look all that bad, with a bit of oil added on it to prevent further rusting. What jumped out at me was the missing removable bit of ways near the chuck. Not sure that's still around or easily put back if it is. It wouldn't be someone's only lathe for precision stuff, but the extra swing and center distance might be a useful complement to something like an HLV-H.
The dealer is a decent and honest guy -- and I suspect it actually would clean up to be a decent lathe. Biggest surprise, for me, is Bob (the dealer) writing that this might be made in Canada. He's handled and even repaired several Harrison's before. Could also and likely be someone else did the listing. I'm pretty sure it's English-made, like every other Harrison I've seen (or owned), up to the 600 Group purchase of Harrison (and Colchester) and the much later move to manufacturing some models in China.
As for salt air -- I see damage to things like steel and even aluminum framed windows along the coast. But I've seen maybe a hundred lathes in various places around the Coast looking nicely oiled without a bit of corrosion. And others a thousand miles inland rusted solid. That lathe was probably bone dry of oil on the exposed surfaces, maybe with a coat of garage dust and sawdust, and subject to condensing humidity. Salt air wouldn't have helped, but it wasn't the cause IMO.
Just as an aside, when I lived on the East Coast cars would rust out in a few years. On the West Coast, cars I've sold to neighbors and friends still look near new 30 years later. Some of that is better rust proofing. But overall I'd sure rather taste a bit of salt in the air with waves crashing on this coast, than drive on salted roads elsewhere.