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Somewhere there is a January 30, 1776 Muster Roll for Captain Benjamin Weiser's Company in or at Philadelphia. Listed on that Muster Roll is a "Leonard Kerstetter" who could be the same person as Joh. Leonhardt Kerstetter, Sr. George Peifer (Pheiffer) was also in the Company. In 1787, Leonard, Sr. had a son George baptized at Himmel Church, near Rebuck (Northumberland County, PA), and George Peifer (Pfeiffer) and his wife Magdalena (Shaffer) were the godparents. I've not yet located this Muster Roll (haven't even gotten around to looking for it yet to tell the truth), but I found its reference in an old journal of one of Leonard's descendants (R.F. Long). No idea if this helps with what you are looking for.
You might also want to take a look at Steve Kerstetter's book "The Kerstetter Family - The Early Years 1727 to 1850", Third Edition, PA State Library-Genealogy Section, 1996. Sorry, I don't have the call number.