I have yet to see a Volvo engine with bad valve guide seals so I'd doubt that guess. It's more likely a clogged flame trap or clogged hoses to the flame trap (PCV system) that'd be causing excessive oil consumption.

How often is the engine burning 1 qt of oil bacause it's not considered excessive unless it's less than 1 qt per 1000 miles.

If the PCV system is known to be good, than have the engine checked with a cylinder leak down tester to try and determine if it possibly has bad rings. Valve guide seals usually do not cause excessive oil consumption if and when bad but might explain oil smoke when started cold or after adding oil as that's when the oil would seap by those seals, not under full throttle.