[dmac]

The dealer wants to sell the car, and the mechanic wants to get a rebuild project - you cannot trust either. If the car has not been driven much lately the compression may come back in a few thousand miles. Noise in the valve train is normal - but you may need valve adjustment, or perhaps a new tensioner - neither are huge projects. Don't put additives into the engine. I say get another opinion - someone knowledgable about 911's but who has no vested interest in your transaction.