Stray thought...... at the risk of making a fool of myself, why don't you take the sender unit to a fitter and turner and get them to work out what thread it is? you might even be able to get them to give you a qote on turning up an adaptor, or recomend where you can get one off the shelf. or, if you can, lay your hands on a set of thread gauges and a vener caliper and work it out. I think nissans usually use metric thread types, but to be perfectly honest I really don't have a clue.