The common problem we see with S/V 40s is that the rear brake pads rust to the calipers causing noise and pre-mature pad wear. The calipers themselves aren't the problem. Remove your rear brake pads, file the rust from the calipers and carefully grind a little metal from the sliding edges of the pads (if not worthy of replacement that is). I grind off a little metal even with some new pads if they're fitting too snug in the calipers because otherwise they'll surely rust in place.

Put either Volvos silicon brake paste or a good anti-squeal brake paste to the backs of the pads, add anti-sieze to the sliding surfaces and re-install making sure that the pads aren't too tight in the calipers (IE: they should move in/out freely, not need to be pounded in with a hammer like you usually must do to remove them).

Many years ago many cars lines included a "brake service" as part of some maintenances like a 15K service but those days are gone, Volvo doesn't suggest that in thier services and if a dealer adviser suggests that (being unlisted), most customers then perceive that as being some sort of rip-off scam. It'd be a good idea though, something I'd do to my newer car.