how do i change oil cooler on astra 1.7 dti?

Hello,
I'm getting a lot of oil depositing around the sides of my header tank, not so much now I have bypassed the oil cooler and done a flush. I believe the problem is the cooler. I have looked at the Haynes manual and it is a bit vague. It states you have to remove the whole oil filter housing and oil pipes that I cannot see or feel very well. Looking online for an after market oil cooler I see it is merely a box with two water pipe spigots that appears to just be held in place by 4 screws. I would like to know if it is possible to just swap this part leaving the complete housing in place.