kk, I have pulled the cowl off to just have a quick look to look for anything air related, the gaskets are intact with no marks, the diaphram isn't what I would call hard but it does have a stiffish feel to it, there are no black marks where oil has been or ever was outside of the motor.

I am going to put a new diaphram in it and see what happens, I will open this thread back up after my next flight which wont be for 2 weeks, keeping my fingers crossed this is the issue. I knew a hard diaphram could cause issues but I wouldn't have called this one 'hard' by any means, hope it IS the issue however.