I am rebuilding a 1985 300d turbo engine. I am on the last piston right now and while looking at the oil ring with my kids magnifying glass I think I spotted a difference in the profile top or bottom? None of the oil rings were marked top side as was the other rings, and visually I could see no difference before being magnified. How critical is this? They are Goetz rings. Please tell me I dont have to remove the other four pistons and check. I want to do it right. Thanks