Rising water in the expansion tank

[The Aardvark]

Hello

I currently have the above issue with a TVR Chimaera with a 4 litre Rover RV8 engine.
It's been a bit of an ongoing saga - apologies for the cut & paste, but I've summarised it here -

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Before the engine is stripped down again, I'm posting here on the off chance that someone may suggest something else to check?

Would appreciate any comments.
Many thanks.