The buzzer not working won't affect oil delivery.
The oil drips out of the pump & into the fuel line before the carbs. Don't expect to see oil squirting out of the pump delivery as it isn't under high pressure.
If there is oil in the top tank - the one on top of the engine - then it should feed to the pump.
The top tank is fed from the main tank in the boat which is pressurised from the crank case. Follow the lines from this tank & you'll see where it goes.
How have you established that it isn't delivering oil?
Try removing the oil pipe at the 'T' junction with the fuel line, plug the fuel line & start on premix to see if oil comes out of the oil pipe.
The usual advice is to remove the lot, fit the blanking kit - the long plastic plug is to prevent a bush coming loose inside the engine - & run on 50:1 premix.
I don't recall seeing any where it has been recommended to keep this system but plenty where it has been claimed to have totalled the engine.
Seen one post where the owner connected a pipe as a loop from the pump outlet to the pump inlet. Filled said pipe with oil to lubricate whatever the oil would normally lubricate & runs on premix. There were no subsequent posts as to how well this had worked though!
I recently had to replace the small tank cap on mine - top split on the old one - & seriously considered converting as the cap was just over £100 so I suspect I've viewed all the same threads on the various forums that you have.
Have a look at this thread from some years ago. The same pipe on my Black Max 135 split in much the same place as on his one.
I only saw it out at sea when I was drifting (fishing) & wondered where the oil slick at the back of the boat was coming from!