Motorworks West tells me it is a double chain and NEVER needs replacing. The previous owner had the car serviced and modified with a Dinan Exhaust cam gear and the shop (Redline In Pompano Beach, FL) said it DID NOT need replacing. I now have 160,000 miles on the vehicle. Do I replace it or not? I need the facts. Is it a single or double. The ETK has parts for both.