Welcome to the forum.
I hate to say this, but I think a third opinion may be prudent. Ask your coworkers and neighbors who they trust to work on their cars and then let him take a look at it. Hopefully it is nothing more than a leak in a coolant line.
2005 SL AWD, Platinum
-OEM HID conversion & HID fogs
-OEM iPod interface
-Upgraded (non-Bose) speakers - Pioneer TS-A1702C & TS-G1643R
-Muth signal mirrors
-Valley Industries hitch and wiring harness
-Aluminum fuel tank shields