In this case, I was put through to Spotless Maintenance, and the bloke I spoke to scratched his head a bit because this vent pipe is not listed in his system as a current asset. It might be in this condition because it was taken out of production years ago, and everyone has forgotten about it. He eventually managed to log a job against it, and we'll see what the crew says about it when they pay it a visit. It was a bit hard to explain the location, since it is 100 metres into a big park.
The good news is that the bloke taking the call was very helpful and friendly, and really went out of his way to take care of a pretty unusual problem.