If you got flow at the radiator, then pump and torque converter are fine. Did you loose Drive and reverse at the same time?

Disconnect the vacuum modulator at the modulator, and see if oil dribbles out? Pull vacuum on it, or attach a hose, and suck on it, yet might hear the diaphram, but that is not a big deal if do not hear it, the driping oil out of the nipple is a big deal.

The mechanical modulator, the car would run, but not shift, yet you can disconnect it from the throttle linkage...

A loose valve body can do this

A worn B2 piston seal can do this for the forward gears, or a broken B2 piston, and it is on the outside of the transmission. I just wrote about this B2...

http://www.peachparts.com/shopforum/tech-help/370728-722-350-4-speed-automatic-slipping-under-load-1-2-3-reverse-solid-4th.html

Gearbox 722.368 repair manual / tips - Mercedes-Benz Forum

All the best,

Martin