Sorry for the overly large delay. I have in my tree a Johannes (John) Bohn but his dob. is 1786.
areas to look in might be Schwartzwald church records, the PA church records, altho I didnt find a lot that was of much help there.
My biggest break came when I was following up on the siblings in the census repors, I found one living with her uncle, looked for his name in the family trees and boom all I wanted to know was there. I now do a lot of tracking of the siblings whenever possible.
Best of luck to you, I know how hard it can be.