You may be very fortunate to be researching a very rare name.
My mother's surname was Benjestorf, and it is also very rare. I had difficulty finding any records, but a telephone book search listed only three living in Germany. I wrote to all three, and one of them sent me a paper, written in the 1950's by a distant cousin, on the origin of the Benjestorf name (it was accidentally formed from another name in October, 1797 !). I now know all Benjestorf's in the world are related to me!
Anyway, the point of writing this was to encourage you to contact those four Bolstorrf people listed in the telephone book. They may very well be your distant cousins, and if you're lucky one of them might have access to genealogical information.
From the Deck of SV CYGNUS
Docked at Jacksonville, Florida