Green’s Dictionary of Slang

1. (Aus.) one of a number of identical manufactured goods, e.g. an automobile, that proves defective.

1993

Aus. Word Map 🌐 brumby ‘I grew up in Adelaide in the 1960s and 'brumby' was an accepted term to mean a purchased manufactured item eg. appliance or toy that was faulty or prone to breakdown and in the sense that it was an unlucky purchase in that another item form the same manufacturer would generally be OK’.

2. (Aus.) a racehorse.

1996

J. Byrell Lairs, Urgers & Coat-Tuggers 235: It is now a negative part of the Australian turf annals that in the ‘82 Chelmsford Stakes over 1800 m [...] with only five other brumbies to beat, Kingston Town failed to run a drum.