You may never see coolant actually leaking. It may never appear under the car.
Try this, get some coolant leak tracing fluid. NAPA of another parts store will have it. Just tell them you want to trace a coolant leak. You'll need a black light as well. Follow the instructions.
After running the car for a while, shine the black light in (at night helps) and you'll see if there is a coolant leak.
My 300E's head gasket started leaking badly and there was little white smoke. Pulling the plugs confirmed the problem. A very wet spark plug in the front cylinder told all I needed to know. If one of yours is unusually clean, that's a good sign something is up. Mine actually hydrolocked the motor (while it was sitting overnight) and that was a sure sign:-) Water shot out of the cylinder after removing the plugs and then cranking the motor. Fortunately, the head is okay and the bottom end is fine.
Net result, getting a valve job since the head is coming off.