A proper steering alignment would produce a car that tracks straight on a perfectly flat road without any crown. Certainly that is how I align my own cars.
In the past some "techs" would dial in what was known as "split caster" which would produce a pull to the left, allowing the car to "climb the camber" of the road. Of course on level pavement the car would pull left. It is a waste of time to do that, especially with modern suspension designs, even if it is possible, given the lack of adjustment on many cars, Volvos included.
Your car may be simply descending the camber of the road in pulling slowly right.
Have a good alignment done on the steering. On the 240's caster is supposed to be fixed, and only camber and toe are adjustable. A good shop will find the way to adjust caster too. Don't "split" the settings - get them as even side to side as possible, and use zero or up to 1/2 degree negative camber.