The M104 engine (AMG variant or not) is notorious for external head gasket leaks on the R side of the engine near the firewall. The engine's front cover frequently develops leaks as well. A lot of extended warranty companies stopped issuing contracts for AMG vehicles specifically becausee of the high cost involved in maintaining the C36. They aren't really any worse than any other M104 vehicle, and with proper maintenance, will run forever. Great car though, tons of fun. The sound of that six in its upper rev range is a thing of beauty.