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I am experiencing gas in the oil of my John Deere L110, Kohler 17.5 Comnand engine. I’ve researched a tech website that identified the cause of gas in the oil as two things: The Fuel Pump needs replacing or the Carburetor needs to be rebuilt, both allowing gas to make its way into the oil supply. Is this correct?

Yes, most likely it is the carburetor, the float needle failed allowing too much fuel into the bowl and overflowing into the engine, drain/replace the motor oil a few times to get all the gasoline out.

After correcting this problem, it is prudent to install a shut off valve in the gas line for extra insurance..

Internal leak in fuel pump is a possibility. Also put a shut off valve on fuel line to prevent carb leaking into intake.

Gas typically enters the engine oil because the fuel tank is mounted ABOVE the carb. In these instances, GRAVITY is constantly pushing fuel against the float valve inside the float bowl. When any issues (wear, grit, etc.) adversely effect the float valve, fuel will flow down the intake, past the intake valve, and past the piston rings.

Because of this, lots of modern lawn care equipment is now fitted with an "automatic" fuel cut off valve. These fail all the time. And when they do, you have no warning until fuel enters the engine oil. I highly suggest you cut the fuel line and add a manual fuel shut off valve. That will permanently end this problem. They cost well under $7 and take a whopping 2 minutes to install. Click to see... Manual Fuel Valve

7394 said:

After correcting this problem, it is prudent to install a shut off valve in the gas line for extra insurance..

Click to expand...

Yep, me thinks so too.

MAK1960 said:

I am experiencing gas in the oil of my John Deere L110, Kohler 17.5 Comnand engine. I’ve researched a tech website that identified the cause of gas in the oil as two things: The Fuel Pump needs replacing or the Carburetor needs to be rebuilt, both allowing gas to make its way into the oil supply. Is this correct?

Click to expand...

If the carb is at fault there will be a performance issue most likely. If the engine performs well until overloaded with gas in the oil, it's likely a pinhole in the fuel pump diaphragm. It'll make fuel pressure to keep the engine running, but will slowly fill the crankcase with gas.

The easy test is to remove the impulse line when you park the mower.
If it has fuel in it and the sump oil level does not go up then the pump was at fault .
Faulty pumps will dump fuel into the engine only while it is running .

If the line has nothing in it but oil an the oil level in the sump goes up ( from the fuel leaking into it ) then the carb is the culprit.
Carbs dump fuel into the sump when the engine is off .

FWIW in 7 years ( going on 8 ) I have only ever replaced 2 fuel pumps.
OTOH I have replaced better than 400 needles & / or seats .

Ethanol fuels can cause the pump diaphragm to deterioriate

So can other fuel additives added by both petroleum companies and individuals. I had a Chevy that would constantly clog the fuel filters as long as I used unleaded plus. Once I switched grades the problem went away.