My Nanni 43hp motor
had a Hurth 100 when I bought the boat. Painfully soon after purchase
the clutches in the tranny failed. Disassembly revealed not only badly worn clutches, but spalling on several gear
faces. Cheaper to replace than to rebuild
, so did so. Vendor failed to tell me that there was a ZF12 now available which was a drop-in replacement, and only marginaly dearer (guess he didn't have one in stock). Anyhow, my manual says that the ZF10 uses
only 350 mL of fluid, and warns to not overfill. I too have a hard time reading the level on the dipdtick,so tend to carefully measure the volume of oil
into a separate container before funneling it into the case.
I also did some internet research
, and found a gripe site for Hurth owners (don't remember where), and the consensus was that you should use Dextron III grade ATF, and change it frequently. So now I do it each time I change the engine oil (200 hours), and have had no trouble in the ensuing 1700 hours of use.
Good luck with it.
Jim and Ann s/v Insatiable II lying Gladstone Qld Oz