But I think I see where the connection is.The famous Knysna pilot that you mention as being a cousin of your Henry Benn, born 1808, is my great-great-great grandfather, born Nov. 12, 1812That could mean that Henry's father William and my g-g-g-g grandfather John (b. Nov. 9, 1786) might have been brothers, both of them sons of Wlliam Benn (born around 1750).
My John Benn, born November 9, 1786 married Elizabeth Day (I think) and his father William Benn (b. about 1750) married a Hannah (but I don't know her last name).
William and John were such common names, but then both seem to have been from Deptford.
You might check too with Annatjie Van Breda who traces her family from William too - email@example.com
Let's see if we can unravel the connections any further.