W220 2002 S430- Loss of ATF

[ytech15]

Hey all,
I've been dealing with this issue for the last couple of months. My 2002 S430 is loosing ATF and I can't locate the leak. I service my 722.6 regularly every 50 K miles without any problems. I replace the fluid, filter, pan gasket and 13 pin connector every "service". Lately I noticed a consistent loss of fluid, When I first noticed it was time to service the transmission and so I did, It was completely dry underneath the car without any visual signs of external leaks. I serviced the transmission and kept track of the fluid level, The service was done 3 weeks ago, and the fluid level was at the blue mark, today it is at the red mark. I checked the coolant - no oil contamination.

Any input?