Found it by luck after standing on the mound in the circle for a while. Was further down the hill, almost in the gully on a much larger mound!
Didn't recognise the name at first and then realised it was the area I knew as Spargo Creek. Went there on a rogaine 3 years ago (which demonstrated that this map is nicer terrain than most of what's around it in general, and the Korweinguboora map used for the 1981 nationals in particular), but otherwise I think I'd have to go back to the mid-2000s too.
Aha - that section of the rogaine was where the 4WDers were camped by the Werribee river and had been churning up the access tracks. Guessing the river wasn't waist deep (on me) this weekend, unlike in Oct 2017?
The river was knee height on both crossings, so you had no choice but to get wet feet. A Long Hard (dry) course version had also been set in case the river was too high.