Leak at AT sender?

[95E320cab]

Yesterday I had my car up on a rack and noticed transmission fluid leaking around what looks like a sending unit for the fluid. The shop tech where I was said he thought the O-ring was bad but that you have to replace the whole sender, not just the ring. Anybody agree or disagree with this diagnosis and if so, what do you call this unit? Can't find it on the parts list of any of the online parts suppliers. Thanks!