[Trackrash]

No way to change an exhaust guide with out removing the head.

Have you considered it could be rings? A leak down test could give you an idea of any trouble or how worn the motor is.

What you might want to try is to remove the valve spring and get a good idea of how bad the guide is. If you are lucky, very lucky, and the guide is within the wear limit, you could replace the valve stem seal and be good to go.

The reality is if one of your valve guides is very worn, you should consider a top end rebuild or at least a vavle job. Otherwise you may have a ticking time bomb.

What year car and what history on the motor?