My buddy has an 86 V20 with a 170 Mercruiser that he rebuilt last summer. He used a rebuilt head he bought from Clearwater Cylinder Head Co. It started missing and running hot. He pulled the head and found it was cracked between a couple of cylinders. Clearwater wouldn't do anything, said his warranty was out. He's looking for a new head (not rebuilt)and we haven't had much luck finding one so far. Do you have any good connections or ideas ?