Ok so I've managed to find out what the issue is with the catch can.
I disconnected the hoses as you suggested and blew through but it flowed freely, no blockage.
I found at idle with all the vibrations, that the cap on the catch can was bouncing up and down very slightly and rapidly, almost unnoticable. I pressed down on it firmly and the fumes stopped. It seems when the cap is shut completely, it's not tight enough to completely lock it in. I also discovered little groves where it makes contact on the inside of the top of the cap.. basically making small indents and making it even more loose. I then discovered that there's a 88mm o-ring on the cap, which seemed to be not protruding enough to also seal in the cap and stop it from bouncing up and down or prevent fumes from escaping on the sides.
I've ordered a new o-ring, but for the meantime I've used some electrical tape behind the o-ring, to make it stick out a tad bit more. It's sealed tight now and no fumes.
My engine bay gets very hot and when I touch the catch can after a descent drive, it's pretty bloody hot. I presume this has accelerated the indents the vibrations have made in the cap.
CatchcanCapSeal.jpg
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