O34 - Portland, OR
I have used a modern ATF in our Hurth with no slippage, for over a decade. I changed to a synthetic version a number of years ago, too. No problems.
Do you use a particular brand/type ? I did find this approved fluid list from ZF who made or bought Hurth(not sure which) and I have been using the Exxon Mobil Delvac 1 fluid which I got at NAPA Auto. But I am curious what others are using.I have used a modern ATF in our Hurth with no slippage, for over a decade.