manifold came off tonight and whilst there was a small tear at cyl 4 exhaust that may have been where it was a bit stuck on the manifold there and to the head in the middle. It's due a coolant change any way so whilst I've got the manifold off and I'm draining it, it seems sensible to pull the head and change the head gasket, at least then I know it's good for however long a head gasket lasts these days