There is a small hole at the front of the engine (on both Rotax 122 and Rotax 123). If coolant fluid or transmission oil leaks from this hole, this is an indication of a leak at the water pump.
Hole on the Rotax 122 
Hole on the Rotax 123
The gaskets of the water pump do not directly separate the cooling water from the gear oil, there is a small space in between, which is open to the outside via the small hole.
The shaft of the water pump is sealed with two shaft sealing rings (10x26x7 WAS). The housing of the water pump is sealed on each side with an O-ring.
If coolant fluid or gearbox oil leaks out of this bore without prior notice, it is very likely that the shaft sealing ring on the respective side is damaged. However, if this happens after an engine overhaul, the O-rings are often not suitable. Some engine gasket sets, which can be bought for low prices from third-party manufacturers, have slightly different sizes of O-rings, which is why they are not always working.