There seems to be two Robert Brooks from Devon born around the same era and this may be the cause of the confusion.
From Lloyds Captains Register Index
BROOKS, Robert Henry b. Devon 1827 C17580 Liverpool 1864
vol.2 1865-1867, 1869-1872; vol.16 no voyages listed
BROOKS, Robert Henry b. Devon 1841 C30045 changed to C012332 (vol.29) South Shields 1869
vol.2 1869-1873; vol.16 1874-1879; vol.29 1880-1887; vol.44 no voyages listed
Brooks seems to be a very common surname in the Appledore area in the period.
I also found this
BROOKS, Robert b. Devon 1808 S36341
vol.2 1856-1857, 1859-1861, 1863-1865; vol.16 no voyages listed.
I suggest you enquire about all three at the National Maritime Museum Greenwich
.Email
manuscripts AT nmm.ac.uk
Give certificate numbers and full names, dates and place of birth.
I understand NMM are not responding to queries until September due to refurbishment.
Meanwhile contact London Metropolitan Archives to obtain entries in LCR for Robert Henry Brooks C 17580 and Robert Brooks S36341
http://www.cityoflondon.gov.uk/Corporation/LGNL_Services/Leisure_and_culture/Records_and_archives/Family_Research/Family+History+Research+Service.htmIf these searches come back negative, I will take a look in BT122/20
William Glass Brooks.
I Know I said to put this one on the back burner but have found some snippets which may be pieces of the jigsaw.
From the Bristol Mercury May 13th 1863.
William Glass Brooks passed as only Mate. Never come across this definition before but it could mean he never passed a masters exam and is therefor not in LCR.
I found a William Brooks GRO Consular Deaths Indices 1876-1880 Vol 6 page 2063 died Montevideo Uruguay. Maybe this may be your family folk law link and may be worth looking at.