After our Tallarook run I found a fair bit of oil has leaked out of the catch can through the tap somehow. circled below. Hard to tell how much oil has actually leaked out as I only spotted it the morning after. Fair bit was on the suspension below and a small puddle on the ground.
Attachment 43295
Attachment 43296

So I took the catch can out completely to re-tighten everything, and re-mount properly as the catch can was sort of just sitting there loosely. (catch can is still out of the car, pipe re plumbed to factory conditions. )

Today I thought I'd clean the air filter and found a rather large oil stain/sludge build up on one side of filter.
Attachment 43297

Unsure how long this has been there for. Could well have been from after that run and may have something to do with the leaking catch can, and it being loose, bouncing around on rough track and sending oil splatters up the air pipe through filter?

As far as I know, oil on filter could be by blow-by? And slightly alarming amount of oil in the catch can is caused by.. ?