AU 5.0 vacuum investigation

[macman]

Got a few things going on with my AU 5.0 at the moment.

One issue is that when accelerating reasonably hard, the dash vents will switch from face or feet over to demist position. So searching the forums here it's quite clearly going to be a vacuum related issue.

Poking around, I followed some vacuum hoses and found a little one-way valve behind the washer bottle. Removed it, quite confident I was about to uncover the problem but it is working perfectly.

More poking around, I discovered a larger hose from the underneath the intake manifold travelling down towards the firewall. Turns out this is my PCV. Anyway, it was oily as hell and the PCV was barely connected, actually just sitting loosely on top of the large grommet it is supposed to be fitted into. I'm not convinced this is causing my problem though. Open to suggestions here.

Last thing I noticed is that there is a rubber gasket between the front edge of the lower intake manifold and the engine block. It looks like this is pushed out, or blown out (see pic). There's no leak around the area (unless it's a vacuum leak) - might expose my lack of mechanical knowledge now...

So my questions, could my demist vacuum issue be caused by the PCV not being connected? And is this dodgy looking gasket going to be causing me troubles?