Help on Oil leak. 1995 VW Jetta

Our 1995 Jetta has a ABA 2.0 engine. It has developed an oil leak between the adapter and the oil filter. My husband is a very good mechanic but he cannot figure how to get the adapter separated from the oil filter. We spent 2 hrs researching on the internet. The local foreign parts shop could not help. Mostly because they do not have a breakdown of the engine that shows this part of the engine. I found a picture of the component on the internet except it did not show the oil filter below the adapter. Our local library no longer has any repair books other than Chilton/Haynes which are almost useless. We will truly appreciate anyone that can tell us how to remove/separate this unit.
Thanks, bettyeh