Blowing Spitfire exhaust manifolds

[waddy@vsfl.demon.co.uk (Simon Waddington)]

Does any one have experience of Spitfire head exhaust manifold gaskets 
blowing?  I bought a 1500 in July and the gasket was blowing then. 
After replacing it it went after six weeks, the one after that has 
just started blowing again!

I've heard rumours that this is a design fault in the exhaust top pipe. Does 
anyone  
know a) if this is true, b) if so what can I do, c) if not what 
else might be wrong.  

Thnxs in advance.
-- 
Simon Waddington