It's fixable if you don't try to run it that way.
The carburetor float needle is leaking, allowing gas to continue to flow into the carburetor, and from there out the main jet, and into the intake, and into the cylinder, and from there into the crankcase.
Disassemble the carburetor and find out what's causing the float needle to leak. Could be crud in the fuel causing the float or the float needle to stick partly open. Could be a worn/leaking float needle and/or seat. Could be a float that won't float anymore. Gotta get this right or the problem will keep recurring.
Once you figure out the carburetor problem and get it fixed, drain the oil and replace it with fresh oil, and you're done.