Marine Transmissions, ZF/Hurth Marine Transmission Sales
For a listing of ZF/Hurth gears...
When you say you 'filled' the gear.. be aware that 'full' is a mark only about 1/4 inch up the dipstick, and should be checked without threading it in.. ie.. drop the dipstick in the fill hole and let it rest without turning it in. They only take about 1/2 liter or quart ( possibly less for your smaller model).
Whatever gear you chose, be sure to check the exit angle wrt to the engine plane, the adaptor/bell housing pattern, crankshaft spline, overall length and coupling bolt pattern for compatibility. Large differences can lead to a new/modified prop shaft and coupling, mount relocation, etc that can cause costs to spiral out of control.