I had to double checked the torque specs and you do have them correct but while looking at the manual it did say not to use the old gaskets. I am afraid it may be the gasket that is the problem now
I would hate to see you tighten the bolts more than the 18 foot pounds and either strip out the threads in the head or break another head of a bolt off.
The call is yours and I know it is not cheap to get the gaskets sent to Portugal but I would get the new ones and do it right and hope for the best
Good luck, Ed