Wow, if they manage to find out who did this, goodness me.
$10 bux says it's a local, probably an Otford local. Woman, 45ish, I reckon she lives near that viewing spot there, where you can see down the coast. She is recently divorced, she has a part time job in Engadine to which she catches the train and she is pretty soon about to have quite an extensive collection of used, worn out automatic transmissions and transmission casings.
Bullshit aside, it was most likely someone who has been activated (driven to action) by hysterical Today Tonight/ACA coverage of "hoons", particularly in the NP, putting oil on the road is, to me, akin to tying fishing line neck height between two trees on a trail up the bush because you don't like the pushie riders who go up there, if they find this person, I hope they are bought before a court to face some serious charges.