The present owners moved into an assistant living situation and the listing broker only is giving out that it's a shared driveway. The neighbor didn't give any indication that he knew he had any legal rights (I was under the impression that he was assuming he had none). He's got no written proof that he does. Whether this might fall into some kind of grandfather clause or not I would confirm with an attorney.
I don't see how this arrangement would be acceptable to anyone buying this house. It's a large home so one would expect at least 2 cars for the new owner and there's not a chance in the world they are going to want to park in the street when they are buying a driveway. The house listing is advertising 6 parking spaces.
I'm going to take one more shot at speaking with the neighbor. I don't see how I have anything to lose. I'm just going to lay it on the line that I wouldn't be agreeable to the arrangement nor do I foresee how anyone else would. He's got to have contemplated this when the present owners moved if he doesn't feel legally entitled. If so, he's already got a back-up plan. I'd rather move somewhere else if there's going to be any animosity. Then that puts the ball back in his court. He said he's going to be living there forever so he can make the gamble on who his new neighbors will be. He very factually could get some less-than desirable neighbors moving in given the condition of the inside house AND still need to more his parking. If he doesn't seem to be generally cooperative I'll move on.
If he's willing to work with me, I'll go forward and speak with everyone you're recommending to make sure I have all my bases covered so I can get my offer submitted.
Thank you very much for all of your input.