Rory
I did not find any mention of Van Musschenbroek/brook in the LTG in G.W.Lines' "Ladysmith Siege" booklet. Nor as a resident.
If you go to WO100/301 sheet 4 you can see his NCOG roll entry (clasp Transvaal) and his name is transcribed as pretty much a squiggle in a couple of places.
Doubtless a detailed search on the ASC rolls could get you something more.
Buxton tells us that members of the NCOG had the honorary rank of sergeant. However, special legislation had to be enacted to allow them to operate outside of Natal. Their medals are usually impressed to "Intelligence Dept" (but not always) and that body was absorbed by the FID in due course.
You should be able to make something out of what has been found so far.
Chalk up another one for David Buxton and his Book "Field Intelligence Department".
IL.
