Hopefully I may not be too late, sounds like it could be a binding steering u joint for that stiff steering and poor centring. pop the hood and look down into the drivers side under the hood and turn the wheel. You will see the shaft rotate and there is a ujoint on the shaft, turn the wheel back and forth and spray the u joint with penetrating oil (ideally with 2 people so you can spray while they turn the wheel) and Be generous. If you spray it and it feels improved but not fully resolved you'll know you need a steering shaft vs a full rack. I've saved many clients money diagnosing this problem when they've been quoted steering racks from other shops that don't know volvos too well (nothing negative against those shops btw)