Hi,
I have a mechanic friend who has told me that it is common to have to change that gasket twice withing the usual lifetime of the car. The first occurance is usually around 80 to 90k and the second around 160 to 190K.
Mine is about due.
To my knowledge GM has not offered any funds for reimbursement. Which is one of the reasons I will probably never by a GM product again.
Best of Luck,
Steve.
PS. Yes, your mechanic is correct. They have upgraded to metal.
Just as a side note a Formula One fan who is a coworker says that they use O rings within a groove on those heads and manifolds. That is basically what the gasket is trying to accomplish through compression, but the crap gasket breaks down and the anti-freeze leaks through.