This is sort of a rant, and genuine question..so here goes:
In the 1970's, GM brought out a lovely little car called the Vega, with its great unlined aluminum block/iron head engine, and a too-small radiator. This caused well-documented diasterous problems such as worn cylinders, overheating, blown head gaskets, and warped and cracked heads all over the place. GM thought it had researched its metallurgy and design well, but apparantly it hadn't, and the car became synonymous with unreliability in short order.
OK, well, everyone is allowed to make even a big mistake, and kudos to GM for trying. Live and learn.
Then GM tried again in 1982 with its subcompact J-cars. One of the engines availiable in these cars (Oldsmobile and Pontiac versions) was a 1.8 (later 2.0) litre OHC 4-cylinder motor with an iron block and aluminum head this time. Because of the different expansion rates of iron and aluminum, again this engine became well-known for blowing head gaskets, and possibly ruining the motor in the process on many cars. Anyone who has been around these cars has seen at least on example of this. Still, GM kept producng this engine for over 10 years; I don't know if they replaced head gaskets/engines readily under warranty. But it still made the car get a bad rep for reliability.
Now, here we are in the early 2000's, and GM is having a problem with...you guessed it....gaskets and metallurgy, and the expansion rates between iron, aluminum, and now plastic has come into the mix. Because of this, engines are leaking coolant from the intake manifold gasket into the motor, and in many cases, ruining the motor. In a best case scenario, the owner may be stuck with a repair bill for the gasket replacement.
You would tink that after the fiasco with the Vega engine and all the bad publicity it generated, that GM would have invested a lot of research effort into metallurgy and gasket composition, and not let it happen again. And when it did happen again on the OHC engine of the 1980's and 1990's, they would have had another opportunity to learn from it and make sure it really didn't happen again. But here we are, again.
This is not meant to be an anti-GM rant, I like their products, and my reaction to it is a disappointed "aww, c'mon, don't let this happen again! You can do better than this!" But its hard to have sympathy for a company that simply refuses to learn from its mistakes, especially the same one, over and over again.....