Youre doing all this with the same possible bad injector?? Obviously the oil is getting fuel in it.. Either from the bad injector, a sensor, or bad ECM thats telling the injector to send in excess fuel.
Do you have a service manual? If not get one or take the machine to the dealer.
In the mean time, I would stop using the machine and changing the oil.
Did you buy it privately? Sucks but the guy that sold it to you was probably aware of the issue, or its very coincidental. Definitely don't sell it to someone without disclosing this info..
The problem isn't major, its an injector, sensor, or ECM, not a bad engine - yet.. Using it with fuel diluted oil can and will cause engine damage.