Hi Rob. First, had you taken the oil separator (circled in green) out and put it where it is? It has to go in the PCV compartment, at the tip of the green arrow. Its purpose is to strain out the oil from the ventilation gas, and return it to the crankcase through the tiny return hole.
[Linked Image]

Second, the pale yellow disk (circled in red) is of a different and I think inferior design to the Honda one. Honda uses a hard flat brown plastic disk, which looks fibre-reinforced. After a very long time, the Honda one wears somewhat in the center, where it hits the stop circled in yellow in the above picture. To see whether your disk is in the right way up, look at its center to see which side has been in frequent rapid contact with the stop.

Here is the Honda disk:
[Linked Image]

I think I'd be inclined to fit a genuine Honda disk.

Have you read this thread?
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=49601&page=2

Way down at the end of it there is an explanation of the Honda PCV system.