2000 SUZUKI DR-Z400S Engine Problems

THE HEAD GASKET ON MY DR-Z400 BLEW AT 45 MPH WITH ONLY 4100 MILES, I USUALLY ONLY DRIVE THE MOTORCYCLE DURING THE SUMMER, AND I ALWAYS PUT NEW OIL AND NEW RADIATOR FLUID, AND DO ALL MAINTENANCE BEFORE I TAKE THE MOTORCYCLE OUT FOR THE YEAR, I WAS TRAVELING ABOUT 45 ON THE ROAD AND THE HEAD GASKET BLEW OUT, WHEN I GOT IT HOME AND TOOK THE HEAD OFF TO REPLACE THE HEAD GASKET, IT HAD PITTED ON THE UPPER AND LOWER SURFACES OF THE HEAD WHERE THE HEAD GASKET FITS FROM HOT GASES. HOWEVER, AFTER TAKING ALL THE ITEMS TO GET DOWN TO UNTORQUE THE HEAD BOLTS, THE HEAD BOLT LOCATED NEAREST TO THE EXHAUST MANIFOLD WAS NOT TORQUED DOWN AT ALL, AND WAS LOOSE AND WAS NEVER TORQUED DOWN AT THE FACTORY. I HAVE WORKED ON COUNTLESS MOTORCYCLES AND AUTOS OVER THE YEARS AND HAVE NEVER SEEN...