Here's what turned out...
I had the car towed to my Mercedes specialist (Mercedes Centre Ltd. in Santa Cruz, CA.) who called me up later in the day and said, "You're a lucky man this time." It turns out that the trans pan gasket didn't pinch and deform but actually tore in three places (at the flat parts, not at the "lips / wings"). They told me that I had "messed it up"...
I was extremely careful when I put the pan back up. I hand-tightened the six bolts first, then used my torque wrench to carefully torque the bolts to the correct spec. I know how to use a torque wrench and have done many repairs / maintenance that was much more complex than this. I suspect that the gasket failed for some reason.
I was also SOUNDLY CHASTISED for changing to Mobil 1 synthetic ATF by the mechanics. They said NO NO NO, DON'T USE SYNTHETIC IN YOUR MERCEDES BENZ. Donnie (and others), do you have a comment or STRONG opinion on this too?!?!?
Scotts Valley, CA.
1993 300 CE Cabriolet (A124) 131K miles
1997 C-280 133K miles
2000 BMW R1100RT 69K miles
1989 300 E 216K miles (sold)