alanhess...
You are a long way from Jake Raby to help you (other side of the pond).
I don't know where you are situated in the UK, but you MUST get professional advice to your problem - and not just from an OPC outlet who will insist on an engine replacement.
You can try Hartech in Bolton, Lancs, (
www.hartech.org) who seem to be doing good work similar to Jake Raby, another is Autofarm (
www.autofarm.co.uk).
Whatever, let us know the outcome of the problem.