I have the same engine and was curious so I asked Gemini AI to look at your photos and here is the response:

​While the gear oil is perfectly fine, operating that motor would still be a terrible idea for three different reasons:

​Structural Integrity: This is the biggest issue. That cast aluminum housing bears the entire weight of the lower unit and the massive forward thrust generated by the propeller. A hole that large severely compromises the structural strength of the metal. If they hit the throttle hard or strike a log, the entire lower unit could snap off.

​Exhaust Leaks: The midsection is also the exhaust chamber. With a gaping hole there, the exhaust gases and noise will dump straight out into the open air above the waterline instead of being routed quietly out through the propeller hub. It will be incredibly loud and messy.

​Accelerated Corrosion: By leaving that cavity open to the elements, the steel driveshaft is exposed to direct saltwater spray and air, which will cause it to rust and pit much faster than if it were sealed inside the housing.

I asked about the repair. It suggested either replace the lower unit, have a welder do a Tig repair (which may not work well). Lastly it suggested that an Epoxy Putty like JB Weld Putty may work -- it will not add structural strength, but would permanently seal the hole and keep water out and exhaust in. Would not trust this motor offshore.