Hello Jose,
Many thanks for your quick reply, and for the inspiration to check the name of the sender and the Comptoller's office. I should have thought to do that on my own. Getting old, I guess.
Following your suggestion I found a single Google entry that contained both Contraloria General de la Nación and Adolfo Weisshaar.
http://www.pgr.gob.ve/dmdocuments/1948/22773.pdfThis linked to a 1948 issue of the Gaceta Oficial. Both names do appear in that publication, but they are not related. There is a record of a decree of the Contraloria on page 8, but Weisshaar's name comes up (also on page 8) only in a proceeding of the Tribunal Nacional de Reparaciones de Guerra where he is a witness to the non-culpability for acts of aggression by a German subject.
Looking further, by Googling "adolfo weisshaar" Venezuela, I found an entry at
http://www.cenco-zotti.com/QuienesSomos_ng.php that begins "It was on November 17, 1949 that three visionary entrepreneurs, Henry Kaufmann, Adolfo Weisshaar and Heinz Petzold, and just in the aftermath of the 2. World War, founded CENTRO QUIMICO, S.A.CENCO. The original mission was to represent Venezuelan and foreign companies and to distribute their products to the chemical, pharmaceutical, veterinary, agricultural, food and flavour and perfume industries."
Various other, later, Google entries identify Weisshaar only as Citizen; not in any official capacity.
While it is possible that Weisshaar did have an official position during WWII and became a private businessman after the war (we have a big revolving door between government and business in the US as well), so far I am not able to document anything but the post-war businessman part of the equation.
I would say that at this point the question is still open as to whether the handstamp indicates some sort of official currency control, or the (mis-)use of an official handstamp (or even the use of a private fabrication) in an attempt to evade US censorship. If the latter, it certainly failed, given the examination of the cover in Miami. More examples of this handstamp (or similar ones) would certainly be useful in deciding the issue.
Dann