Dear j.pelchat,

Hope you're well. These eight nuts are "mission-critical". If they fail, you have exhaust leaks and have to repeat the gasket replacement job.

U.S.-based Volvo dealers sell these nuts for about $3 each. For an extra $4 (€3.50) for a set of four (versus the after-market items), I'd buy the Volvo brand nuts, install them, and drive with confidence.

To ease removal of the in-service nuts, wire brush the stud ends to remove rust and then saturate the studs/nuts repeatedly with PB Blaster, Kroil, or other penetrating oil.

Finally, I'd coat the studs with a nickel-based anti-seize (good to at least 2000°F). This will ease removal, when inevitably comes the next time...

Hope this helps.

Yours faithfully,

Spook