I replaced the sender last night ... it was a serious PITA, although not at all complicated. Just a matter of getting a wrench on the bolt. I ended up breaking it loose from underneath (needed a stubby 17mm), replacing it, then tightening it from above because I didn't have the hand strength with my arm extended that far from below. I think I got it pretty tight; it hit a point where there's no way to fit the wrench on it and still turn it, but I had to push it pretty darn hard to get it to that point so I'm guessing it's plenty tight.
Anyhow, there's nothing leaking down the side of the engine anymore and much less on the TC, but still a little dribble coming from the seam between the TC and engine, and looks like some coming out of the TC. It's definitely oil, not ATF. It's very little, not even enough to drip onto the ground (so far). Will watch and see.

Random observation: The old sensor, when it came off, had a funny gaseous smell. My oil does not have this smell ... in fact I recently had it tested and there were no contaminants. Why did the sensor stink? The new sensor also reads a little differently ... a hair lower at idle and seems more sensitive to little fluctuations. Pressure looks good though ... 3 bar at ~1200 rpm or above and about 1.75 bar at idle (when hot).

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)