Complex sentence: The word koala "comes from the Dharug" gula' "oo" (in spellings such as "coola" or "koolah"), it was changed to "oa", possibly in error.
Split into simpler sentences: The word "koala" comes from the Dharug "gula". Although the vowel'u' was originally written in the English orthography as "oo" (in spellings such as "coola" or "koolah"), it was changed to "oa", possibly in error.