Looks like your throwing parts at it instead of basic diagnostics. Fuel pumps ,injectors and regulators are highly reliable and rarely if ever fail.
Oil pumping out the breather is an indication that your scavange pump is not working. The oil is being pushed out the crankcase from the breather system. Thats also the reason your fouling plugs as its going through the rings.
The engine needs what ALL cannondales need and that is a basic rebuild by someone who knows the basic updates or willing to learn. Its not hard and doesnt cost a lot but it has to be done. After being done they should have as long and reliable life as any other sport quad.