i have a c85trls -, found #3 sparkplug was not firing had small amount of rust on it. motor ran bad, i was told on this forum to pull head and go from there. i did, all cylinders look good (smooth bore) lots of corrosion in water passages. cant tell by visually looking if head is warped or not. do i need to go to machine shop ? i see what looks like small cracks around combustion chamber (around bottom of sparkplugs) but a friend says they look like casting flaws, is this possible? also removed plate that is bolted to head with water jackets, it is also corroded. i need to change that gasket also but dont know what you call it. any reply is appreciated