Hello, I have a 02 Grand Prix GT (NA) with 205,000 on the block. Recently its been making a very slight knocking sound coming from the rotational assembly. (Pistons, Bearings, wrist pins. Not sure which one yet) i am an automotive technician, spent three years in college for auto and worked in a dealership for two years. My main question is I have heard you cant replace just the rotational assembly in this motor, is this true? Can I replace just the pistons or bearings (or what really is knocking) or do I have to replace the entire engine. Oil change is up to date and done religiously at 3k.