Update...
The actuator linkage popped off again. This is a ball-and-socket connection at the swirl flap motor, and clearly the socket has gotten tired over 275k.

This is a 4 inch long linkage, with ball-and-socket at each end. I called MB dealer to get a replacement linkage. They confirmed that that linkage is part of intake manifold assembly, and only sold that way. I challenged them that this is a linkage that is easily removed by hand, but they confirmed that there is no part number for just the linkage. Intake manifold is about $1k, and there's no way I'm replacing that due to a tired 4" long linkage.

I took Catalind's advice to drill carefully through the tired ball-and-socket on the motor end, and feed a wire through, to act as a keeper for the connection.

...easier said than done. There is not access to drill the motor arm with the motor installed, so motor removal is necessary. Removing that motor is only 3 torx bolts and electrical connector, but extremely painful to access. I can only reach near it with left hand, and it ended up being me topside reaching around the manifold, and my wife's small hands on the creeper underneath to get a wrench on those bolts. I seldom have to summon the wife to the garage to help.

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Mark in MA
05 MB E320CDI 402k Granite Grey Metallic
05 MB E320CDI 267k Black
05 MB E320CDI 232k White
05 MB E320CDI 209k Tectite Grey
99 Dodge 2500 Cummins 5sp 148k
62 Jeep CJ-6 120k