I am having issues with my M54B30 3.0i in my 2003 Z4. Possible diagnosis centers around either a head gasket failure or loosened head bolts (would require Heli coil installation). Has anyone repaired these issues in this engine? What level of difficulty have you encountered? What was you success rate in terms of a successful repair. Number of miles since repair. Should I do this repair on an older Z4. Thoughts on buying a replacement engine on E-Bay for about $1,000 and installing?