None…sounds like your diagnosis maybe straight out of your manual? And you know how life goes …theory versus what actually happens to us or in this case to our Disco's can be surprisingly different. If it was me I would find an experienced 2nd opinion if possible. Other causes come to mind…gaskets, incorrect torque etc. However I don't have any first hand experience with a blocked PVC system, I wish I did so I could be more helpful & less advisory
...I pretty much only know what I have had to fix or get fixed and what I still need to get fixed.
