Here is a place to get some Hofner advice. These guys really know their Hoffys.
Be patient-sometimes the site is down.
http://www.hofners.co.uk/
You could also contact Hofner themselves and see what they recommend.
You want short scale strings for a 30" scale.
Labella makes flatwound strings specificially for Hofner basses.
Thomastik makes Jazz Flats that fit Hofners (set JF324)
Pyramid of course makes strings for Hofners but they are expensive and not that good.
Check with the people on the Hofner site first to see what the problem is with the nut.