Using oil issue
Make sure it’s not pulling oil through the PVC system.
I’ve seen engines leak pretty well (under 15%) that used oil like a mother.
Most of the time the second ring was killed and the oil rings were marginal at best.
Not saying that a compression test and a leak down shouldn't be done but let me relate what happened to a customer last summer.
Customer bought a new 602 crate from us and had us dyno it. Motor dynoed fine and made slightly above average power for a 602 crate.
He put the motor in his race car and it ran fine the first couple of nights. Soon following he noticed a miss in the feature. He pulled the plugs and had one that appeared fouled. Replaced the plug and the motor ran fine the next race but at the following race started missing again. He pulled the plugs and the same cylinder was fouled again.
This time all cylinders were compression checked and leaked down. All cylinders checked good in both compression and leak down. Customer tried a different carb but in about 2 races the plug fouled again.
We borescoped the engine and the cylinder in question looked like the other cylinders. Nothing out of the ordinary.
The motor was still running great so the customer finished the last few nights of the season preemptively replacing the sparkplug.
At the end of the season the motor was taken to a certified crate rebuilder who repeated a compression, leak down and bore scope of the engine. Finding nothing the motor was disassembled. It was discovered that the oil rings were mistakenly left off the piston from the cylinder in question when it was assembled new from the factory. Only the top and second rings were on the piston.
My take away from this is that a compression or leak down test are not good indicators of the condition of the oil rings.