Well, I took the car in last night to the MB service center. After sitting all night, they said there was so much pressure in the overflow tank, they were surprised the cap didn't break off. Definitely a head gasket problem.
The quote on the phone said 17 hours of labor would be involved. That really seems excessive, does it not? At $80/hr, that adds up rather quickly. Also, that didn't include the machining of the head which is done by an outside shop.
Since the head and gasket were replaced not too terribly long ago, what could have caused this to happen? It didn't ever heat up excessively, at least not to the point of reaching the red area on the gauge (no warning light either)...
Am I being fed a line or does this sound about right?