Pat, I will speak with Steve Jaffe and see what i can do. Please understand, the 3HP12 hase been out of production for better then 30 years. Industry support for cars past the end of production is only mandated for 10 years. In other words the technical information has been long moved to the "back of the filing cabinet" because there is little to no demand for it. I too have been looking for some information for the 3HP12 in my recently acquired NK. I'm having problems getting it, and I WORK for ZF.
Any manual that may still exist out there is paper or fiche, and will have to be dug out, and scanned etc etc. I think you can appreciate that ZF, like most companies these days, is operating with fewer people doing more. I know Steve and the rest of the people in that department. They are all car guys and would love to help when and where they can, but if they were to try and handle special requests like this from every enthusiast out there they'd be completely buried. We get requests like this every day from not only people like yourself, but from corvette owners, ford truck owners, porsche, and audi owners. Just to name a few. These calls are in addition to all of our "regular" business calls from the OEMs and our large parts customers in the independent aftermarket who's business keeps our lights on.
ZF corporately has recently started a program to support older products, much like BMW MT..er..BMW Classic. Its called ZF Tradition. They are charged with developing programs to support older ZF products in the field. Much like the original MT division at BMW, they are crawling before they walk, and not only have to do it for car transmissions, but for bus, truck, heavy equipment, and so on, and not just for German manufacturers, but for manufacturers around the world! So, not everything will be available immediately, and some things might never be.
To our friend Mr Guest. He might consider that an article published about ZF 16 years ago, might be passed its "best before" date. I certainly wont defend the responses the author got from whomever he contacted at ZF, but I can say that the story is ancient history, and the "issues" with 4HPs were adressed as best as possible at the time. Remanufactured units that came from ZF were always updated to the latest technical specs and were definite improvements upon earlier models. I can also tell you that the 4HP24 in the 750iL's didnt have near the same issue, and were more then capable of handing the performance of the V12. As a matter of fact, a friend of mine has run a 750 in one of the 24 hours of Lemons races, and the car (and 4HP24 trans) ran flawlessly. Subsequent generations of 5 and 6 speec automatic transmissions are generational leaps in technology, and today are incredibly robust and have a service life of many years.