MB agreed to change (on warranty) the valve seals on my engine (I was aware that better seals went into production after my car was built.) to, hopefully, improve oil consumption, which was about a quart every 2K miles, however I elected to wait until just prior to the end of the four year/50K mile warranty, and at about 48K the head gasket began to seep coolant toward rear of the exhaust side, so they pulled the head and completely rebuilt it - all new guides, new exhaust valves, and, or course the newer viton seals.

The engine seemed to pull a little stronger at the top end after the rebuild, but interestingly the oil consumption was about the same, and has maybe degraded to a quart every 1500 since then.

Bottom line as Larry said is that head gaskets that seal materials with different thermal expansion characteristics will not typically last as long as if both head and block materials are the same, and it's a matter of the number of thermal cycles, not miles, so a car that sees low average trip mileage between cold starts is going to have the head gasket go in fewer miles than a car that has high average trip mileage.

Owners of vintage Alfa Romeos consider changing the head gasket at least every 50K miles, if not sooner, as "normal maintenance".

Duke