This sordid topic has been discussed many times over the years. From what I can tell, no one has ever found a satisfactory home-made solution. You have to buy new inner door panels from a Volvo dealership, and even the new panels may begin to separate after a few years. I took my car to an upholstery place, and the owner said there was nothing he could do because of the way the vinyl is stretched into the pocket where the arm rest is located. It shrinks and pulls away. Volvo NA was really rotten in their response to this bit of low-end engineering.