The circuler part of the oil cooler is unscrew able. It has a bolt on top of it I think it's a 19,20,21 when you take it part of has one big orange o ring inside of it that flatins ones it gets really old. Greg v sells it. Also once you remove the oil filter housing from the block replace with new or rtv the old small o rings so you gurantee no leaks. Just a word of advice from experience.