It's called Finnegan Begin Again and was, in fact, the second to last film he ever made. It co-starred Mary Tyler Moore and was absolutely charming. (It also featured Sam Waterston.) The film is somewhat in the vein of "Murphy's Romance" with James Garner and Sally Field. What's odd is that they both were made the same year, in 1985. Unfortunately, it's not on Netlfix, and I'm not sure if it's available for rental anywhere or even on DVD. At least it can be bought on VHS at Amazon, but that's hardly any help for most people. But it's worth trying to track down, at least for my taste. And especially if you're a Robert Preston fan. (And Mary Tyler Moore, too, who's quite good in it, but Preston stole the show. He gives an absolute rich, easygoing, deeply-mature performance)
What I can do, though, is offer a four-minute "Behind the Scenes" featurette that HBO made for the film. The quality isn't great, but it's very watchable. It also doesn't do the film justice, however, largely referring to it repeatedly as a "comedy," showing bits of slapstick It was very funny, but it's much more a thoughtful, wistful romantic comedy that even has a good share of drama.
The clip here shows that it's 10-1/2 minutes, but it's not that long (just four minutes, as a said). Also, it starts about 1-1/2 minutes in, so you can jump forward if that's your pleasure.