After posting the pictures of the PPR, I did some more research on the PPR, I noticed in the photos online, there is a plunger on the end of the pin.
So I had another look at mine as when I took mine out there was no plunger, and found the plunger was stuck inside the dizzy.
Being very careful not to scratch anything, I pushed some rag in there and tried rotating it to see if the plunger would come loose. It didn’t seem to want to budge, so rather than risk damaging it, I figured the dizzy will have to come off. I pulled the dizzy off the air meter and now I can see the plunger though the side ports. There was enough room to get a screwdriver down the port and in front of the plunger. I wrapped some rag around the screw driver and gave the plunger a bit of a push, it didn’t move at all.
I filled the whole area up with penetrate oil (Yeah, I know this will ruin the o-rings, but they are replaceable), and tried some more, it wouldn’t budge.
It’s well and truly seized In place. I notice there is no real way to get into this chamber, so it looks like I need to get it and the CPR rebuilt, as well as look for that blockage in the return line.