93 944ti
Thank you all for your suggestions on changing my manifold gasket.
The bolts werent rusted at all but I lubed the bolts a few days before doing the job anyway as suggested, just in case. None of them broke, in fact, all the bolts came out without stress. Suprisingly, even if it is a Quebec car (Montreal even worst), the whole car is completely rust free (i'm pretty proud of this).

For those of you who has to change that gasket in the future, make sure you get the flat gasket and the O ring of the turbo oil return pipe at the same time.
At almost ten years old, the little flat gasket is very brittle and brakes very easily, so does the rubber ring that secures and seals the pipe in the crank case. I had to wait for the Volvo dealer to open the next week to get those gasket before I could drive it, oil was leaking like crazy.

JF