This is going to be contentious in the extreme on here but here is one simple solution. It's not a repair but it will stop your wet sumping for all time.
https://www.themagnetoguys.co.uk/oil-tap-with-cut-out-switchI fitted one (against all advice) but for me it's been a brilliant and a fairly low cost easy solution. It's a simple on off ball valve. I don't use it unless leaving the bike long enough for it to wet sump. Here is a description of how it work:-
A microswitch is housed inside a nylon body. It's fully waterproof, protected to IP67. A cam plate is attached to the oil tap handle so that, as the tap is turned on and off, the microswitch is automatically operated in such a way that the engine cannot be started until the oil tap is turned fully on.
CLOSED: When in the 'closed/off' position to prevent oil flow, a cam plate makes contact with, and presses down, a microswitch plunger protruding from the top of the nylon body. As a result:- The magneto will be shorted to earth and its not possible to start the engine.
OPEN: When in the 'open/on' position to allow oil flow, the cam plate moves away from, and releases, the microswitch plunger. As a result the magneto cut out will be disconnected from earth and it will then be possible to start the engine.
The shape and position of the cam plate ensures that, even with the oil tap in mid position, the ignition system is still prevented from working. The engine cannot be started until the oil tap is in the fully open position resulting in a completely clear path for the oil to flow through it.
Here's a photo of how I fitted mine (click photo to enlarge). You can see the cable coming from the switch in photo. In my case with lever vertical switch is in off position, horizontal is on (same way the oil flows). It can also be used to cut the engine and that's a good way to test the electrical connection is still ok.
Rog.