I ran my mower for the first time in about a month, never a problem besides old battery. After about 10 minutes on low, flat ground grass, it rumbled and started smoking A LOT and started dying. I let it sit for a few, started again and same symptom.

I checked oil, no fuel that I could tell but does need changing, fuel filter is clear, spark plug DOES have oil on it, and oil is seeped onto base around motor and onto pulleys below.

Is this a head gasket problem?

Thanks in advance.

Head gasket or valves stems are my first thoughts. What is your compression?

I don't really know how to check the compression.

I drained the oil this afternoon, and found that I was wrong about the fuel in the oil. It was there. I drained it all out, ran some new oil through it to purge the old, filled it, removed the airfilter to make sure that wasn't contributing, and then started it. It started right up, smoked heavy for a moment, and ran pretty good. After a few minutes it was pushing some blue smoke, thin but noticeable and constant.

Does this help?

To check compression you remove the plug and install a compression tester, about $17 at an automotive store. Pull the cord several times and record the highest psi reading, that's your compression. A compression test might help to determine if you have a bad or broken ring.