Esterbrooks tend to be scarce here in Australia, a friendly dealer has a J but capless (which I did not get), but today I picked up am English-built red J without nib unit from another dealer; he was cleaning the nib unit but it rolled off the edge of his desk so he will look for it in due course, before the vacuum cleaner snatches it, hopefully!
Right now I have an Osmiroid nib unit, marked "Broad" but is markedly left oblique; I do not know if it was worn down to be as such but the corners feel a bit sharp, for what it's worth. When I screw it into the section front, the orientation of the nib turns past the line in line with the fill lever. As I do not have original Esterbrook nib units, I do not know if they all fit a section with consistent alignment; I would be very grateful if my experienced fellow correspondents can enlighten me on this.
A bit of soul-searching makes me think that the Osmiroid nib unit might not be the most suitable for my purpose, I suspect something a bit more pedestrian such as a 9556 or something along the line; it might be a bit of a wild goose chase here though.