a camshaft seal involves taking of the timing belt the camshaft oil seal is a cheap part its usually replaced at the same time the cylinder head is put back together with the valves valve springs valve stem oil seals and hydraulic tappets and camshafts. if the camshaft oil seal is leaking it will be damaging your cambelt and spraying over all the pulleys under the camshaft timing belt cover and that means a new timing belt as well as any other belts may have oil on them. if its only on the one side of the engine the camshaft cover may have been over tightened or under tightened. the more the engine is run the more it will leak oil . check underneath the engine to see if its sprayed across the underbody of the car i,e cover exhaust,fuel lines,brake lines ,