1085 300CD has 250k miles on it. The vacuum pump produces 29-30 when tested at idle, so it is doing pretty good for producing vacuum. Why should I replace it? I have read that internal parts can break up and that it should be rebuilt at around 200k. After having bought a timing chain replacement kit, I was shocked to find my timing to be perfect, so no need to replace the chain. Any need to rebuild the pump?