For future reference:
While the filler bolt is M14 with fine thread (14mm x 1.5mm), the drain bolt is a M10 (10mm x 1.5mm). There was a lot of half-information about the exact sizing of these bolts, and it is not specified in the service manual. (At least not in the one I managed to find.)
The filler bolt is placed in such a place that it is not possible to get most (all?) clutch-type torque wrenches into where it needs to be, while a standard wrench or even a smaller ratchet would fit without issue. With the right lengths of extensions, you can get the head of the ratchet inside the suspension assembly where this is not a problem. A breaker bar is usable without extensions.
Finally, the filler hole is only a few cetimeters below the sidewall of the wheel well, making filling from the side rather difficult and slow. It is perhaps quicker and easier to use a funnel with a very long hose attachment and filling from above the engine compartment.