I have an issue with my Vectra C. Bad oil consumption. It doesn't appear have any external leaks at all and very little blow by in fact it has a bit of suction under the valve cover. It has a full service history and I changed the oil and filter in August. I have changed the rocker cover which contains the PCV valve. It appears to start and run an is quite drive-able but a bit sluggish for a 1.8 140hp petrol but appears to have torque when pulling away. i am thinking valve stem seals. Does anyone have any ideas.