I was fortunate enough too see Seibel perform in the late 1970s.There was a feature on him in the June/July 1996 issue of Dirty Linen magazine. He performed into the early '80s, but his muse left him (he felt) and he grew increasingly uncomfortable with performing despite an inability to come up with new material. Regarding his career, he said, "I wasn't getting anywhere. So I stopped."
At the time of the article, he was working as a bread baker in a "cafe/store in Maryland," and seemed happy to discuss his career in music. Perhaps he's still there.
Your question ties in nicely with the article's closing lines. When asked how he'd like to be remembered, Seibel said, "Well, 'He was a guy who wrote a couple of pretty good songs. Whatever happened to him?' I guess it's gonna go down something like that."
You can get both of Seibel's great albums through Amazon. Woodsmoke and Oranges (now retitled simply "Paul Seibel") has been reissued by Rounder. Jack Knife Gypsy is available as an import. Fine, fine records.