I recently purchsed a NOS ZF posi-traction unit from an OGTS contact in England for my GT V-6/T-5 modification. The cost was about $1200 including shipping and additional $235 to have the local rear-end pros install the unit in my housing. I understand there are more units available, some from Quaife, at least they promised to make a run for the Opels. the used ZF units in England for should go for around $600 to include shipping, at least that what I was told on the phone. Martin , the contact in England is extremely courteous and helpful. He makes runs to Germany as necessary to get parts. HTH
Ron
Ron