I have replaced valve cover and still have blue smoke

My 1996 4 cylinder Honda Accord has 377,000 kilometers. It exhausts blue smoke for 1 to 2 minutes on cold start-ups. What is the likely problem and are there any engine additives that I can use that will stop or reduce the blue smoke problem but not cause My mechanic has replaced the PCV and also has replaced the valve cover gasket set but the blue smoke exhaust still continues.