The manual says the transmission is shipped with oil in it.
I checked it before first starting, and it was up to the mark
After running a little, mostly out of gear, I checked again, and level was down to the bottom of the dipstick. It took 3/4 of a litre to fill it up. (manual says capacity is 1.9 litres)
No leaks visible. Our bilge is clean and dry.

The ZF manual says that after first running, oil level may drop if oil has moved up into any oil cooler that is installed. We have one, above the transmission.
This make me wonder whether the transmission was actually run in the factory engine test, although the test certificate says it was.
I will be asking Beta about that, hopefully today, but this may be a public holiday in England.