On some blocks (I am talking about all cars, not just Volvos), fastener holes come dangerously close to water passages. Sometimes, because of various issues like casting porosity, there can be leakage around certain bolts. As a precaution, some manufactures use sealants on bolts that are subject to to these issues.

I have no idea if that is the case here.

But if there is such a thing as Volvo Hydraulic Sealing Compound and if you have found a recommendation to use something like that, then I would use some sort of sealant on those bolts. I would think that regular pipe dope, or Silastic, would be sufficient.