What year is your CL63? I believe the OP is basically asking about the head bolts. They were suspect until they were replaced by a new design sometime in 2011. Of course when the head bolts went, you blew the head gasket and the coolant in the engine blew it so you had to get a new engine. If you catch it early enough, you could just do the head gasket or just replace the head bolts in advance. In addition to the head bolts, the M156 engine has a few other issues as well. Not all engines with the bad head bolts went bad.