I do realise this thread is old, but thought I'd add some experience.
I've had a leaking ABF from around the oil filter area for a couple of years now.
Wasn't much to begin with, but lately its been bad.
I noticed it is coming from the oil cooler area which is part of the oil filter attachment housing.
Today, I decided enough was enough. I removed the oil filter, and found the nut holding the cooler wasn't even finger tight.
The nut goes on the same thread as the filter attaches and is 27mm i think. Maybe 24.
I tightened it up and fitted a new filter.
I THINK it has stopped the leak. I will know for certain when the car get MOT'd tomorrow and driven a bit.
Worst case scenario is that I need to change the cooler assembly.