I changed the ATF and filter on the 300e, putting in 6 quarts of Mobil1 ATF. Cold but running, the fluid level on the dipstick only covered the bottom curl on the stick. I was leaving for a trip and decided to drive about 15 miles then check the level hot.
When I checked, there was none on the front or back of the dipstick, but a little on the side. Since I was within 1/2 quart of stated capacity I continued the 200 miles to Knoxville, the car ran fine. I left the car parked for two days there and left for work on Monday.

About 50 miles out at 85mph down a long steep hill with my foot off the throttle I noticed a fairly serious amount of smoke coming out the back of the car. The temp stayed steady, oil pressure did not move, no lights came on. The smoke stopped when starting up the next hill, and did not recur the remaining 100 miles. Everything else seemed normal.

Leaving work that night, the transmission slipped badly trying to get into drive, and during the 1/4 mile limp to the gas station. I put about 1/2 quart of off-brand transmission fluid in (ruining my Mobil1?) the transmission went into drive ok and I headed home. There was some flaring going thru the town about 50 miles away; at the stop sign 8 miles from my house, the trans slipped on takeoff.

I have seen posts indicating a sticking modulator can allow ATF to be sucked into the intake, and this would seem consistent with the symptoms I experienced.

Question is what to do now?
Can a sticking modulator be corrected, or is it simply replaced?
How do I confirm this is the problem?
How much fluid could I have lost on that hill?
I see fluid on the faces of the dipstick with the car cold and off, why can I see none with the engine running?
With the closest MB tech 70 miles away, is this something I should deal with rather than risk driving the car?