It is a well known fact that Guzzi uses some of the hardest Parmesan cheese known to man to make their bolts. I think I have broke at least two. I always replace with a non Guzzi bolt if I haven't already.
Beware of tapping because those castings are extremely soft use lots of oil.
For me all bolts get either anti-seize or loc-tite, Luigi on the other hand didn't seem to think so.