how you replace the valve cover gasket

This car does not have a valve cover, but a two part cylinder head and they are sealed extremely good. I'd suggest to take your car to a Volvo specialty shop, they are familiar with this engine and can help you to figure out where the leak is coming from. Zee

You have to remove the top part of cylinder head and reseal with special sealant. However, ZeeTech is right in that it's a pretty complicated repair that takes a few special tools to get everything back together correctly and without doing damage. Bring to your Volvo specialist.