PA…. Was the ambient air and engine temperature cold when you tried to remove sender? If so, sometimes threaded items of dissimilar material such as steel bolt screwed into aluminum gets real tight as temperature gets low from different rates of linier expansion. In other words aluminum tends to shrink and or expand twice the distance as steel per degree from room temperature. This expansion thing becomes more problematic if the bolt or device was installed on a hot engine. I don’t recall if the oil sending unit is steel in aluminum or not, but it has a funky pot metal shape to get a wrench onto it.
Warm engine up, and try it again.
