I had a similar problem with my 97 960. I fixed it by opening the little trap door that is in the trunk up close to the rear seat. You have to remove some of the cardboard covering to find it, but that is easy. After opening the door, I went with a flashlight to the gas station and filled the tank all the way to full. At that point I could see the gas pouring out of one of the little hoses.
If this hose is your problem, you can get the exact hose (3/8"?) at Autozone etc. You might want two new gas line clips (I used the screw type). The replacement requires a bit of contortion of the hands, some angled long nose pliers helped me a great deal, patience and having to lay at different angles in the trunk to do it. When it was all over, it seemed really easy. As I was doing it, I thought it might be impossible.
I'm not a mechanic either (psychologist), but I am "handy".
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89 244; 97 964