Do you have a chrome after market water neck or the stock neck? I have yet to find any gasket that will work with those chrome types.
The car had a cheapy chrome one and I've fought it
constantly. The new one is billet and was milled at Hawaii Racing here in Simi Valley. It didn't fit my thermostat (not the standard cheapy t-stat) so they milled it down to fit. The rest they make they said would handle all t-stats.
I've heard that people also recommend the billet water neck that Mancini Racing has. Not sure if that is an o-ring unit but people here say they work great.
I've only had one day with this one... will check back in if it fails.
Alan