I would check the inlet manifold gaskets.
I've had a number of attempts at overcoming a similar issue.
http://www.the75andztclub.co.uk/foru...+gasket&page=2
My last attempt at replacing these has been the most succesfull, thanks to advice from Simon (SD1too) in terms of the tightening sequence.
It lasted around 3 months, but has now started leaking again, albeit at a much lesser rate than previously.
To me it's clear they are only just capable of doing the job.
