The rain has finally stopped so I hopped up on the roof to look at the problematic rain gauge on the Vantage Vue. I took it all apart, no blockages that I could see. Made sure that it was all moving freely (I probably should have put some grease on) and put it back on.
It rained slightly last night and the rain was captured so I guess it's now OK (yes I know I should have taken a bottle of water up with me to test after I fixed it).
We'll wait and see if its all OK and I'll have to manually update the rain records from the Nobbys Head figures.