Biggest problem I ever had was the bolts continually coming loose. Only fix was to drill and safety wire them, that is until these came out:
http://store.summitracing.com/partde...2&autoview=sku
The metal reinforced stock gaskets hold up pretty well if the bolts don't back off, the small gap starts blowing off material and next thing you know you hear that popping sound.
Definately check surface of heads and flanges and make sure they're true. Sanding block will reveal this pretty quickly.