Your motor looks like it has a lot of corrosion in it....so it may not be long before it becomes terminal. That said, if it was mine I'd consider removal of that broken bolt and try to build up the area with a weld or JB Weld and button it back up and try to milk another year or so out of the motor...who knows , it could run another 5 years....I guess a lot might depend on how far from port/off-shore you need to go. My C90 is a 1999 model and hopefully the corrosion on the inside is not bad, but I've not had reason to remove the head....so who knows?...