Mine did exactly what yours is doing. I think I tried a little dab of silicone sealer/adhesive, but it did not last long. I finally decided to replace it and was pleasantly surprised that a new seal is only $62, or about $70-$72 with shipping at Tasca Volvo.

Teardown and reassembly/alignment of the sunroof is easy, forcing the seal all the way on to the outer panel is not. The seal has a vice-like grip, and is very hard to get on all the way, and evenly. Your hands will be very sore and tired afterward, but if you plan to take breaks and stretch them it will go ok. If you get it on properly it will be just as good as the day the car was new. Well worth the effort.