Yes that seems to be the most probable cause. I remember seeing a guide somewhere of how to fit a U shaped metallic sleeve, that would stop both belt and cover getting damaged. Will search around to try to find it
Edited: Found it. 4 forty is the one who did it. Will pm him for photo and how too....
Thread is here:
http://www.volvoforums.org.uk/showthread.php?t=9186
Also thanks to Andy_d for pointing out to me the torque settings for the seatbelt bolts. They should be both tightened to 48Nm / 35 foot pounds