I have heard that the new head gaskets have been updated (a few times actually). However, I still recall them known to leak even after the updated head gasket has been replaced (though an extended interval)... not 100% though.
My first head gasket was replaced at 55k miles. I now have 125k miles and not a drop anywhere!
And Paul, don't forget that you can check the coolant to see if there's oil in it, and check the oil to see if there's coolant in it! Good luck
2006 E350 w/ 155k miles (Daily Driver)
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)