Command Pro 25 Oil Burning Diagnoses help

I have a Kohler Command Pro 25HP vertical shaft that burns a lot of oil. Motor has around 300 hours, been using 10w-40 to try to slow oil burning. After mowing for 2 hours, the oil level drops from full to below add. Smokes terrible on cold start up, but no smoke while mowing and motor actually runs quite well once up and running. I replaced head gaskets and ground the valves to re-seat them and I replaced the valve guides. Cylinders looked excellent no scoring and cross hatching looked good. I also found a failure in the crankcase gasket that required splitting the crankcase to repair. After all of this, motor continues to burn oil.

With a warm motor, each cylinder compression tests 145 - 150 lbs.

With a leakdown test at 90 psi I can only hold 32 lbs PSI in each cylinder. Tested each separately while turning crank with wrench to TDC. Air coming out everywhere; Exhaust, Oil filler tube and intake. Seems to be more escaping out of exhaust than other places. Leakdown test was done with shrouds still on engine and engine still on mower.

So, I'm perplexed at where to zero in....

- Worn out rings?
- Bad valves?
- Breather reed?

Since that engine doesn't use compression release the compression readings you obtained are lower than the Kohler recommended 160 minimum psi. Also if you getting air bypass past the valves that can drastically effect the percentage of leakdown. It came be hard to evaluate the quality of the ring sealing ability if the valves are leaking. So the leakdown reading may not be accurate with valve leakage.

Sounds like that head job was not as good as you thought.
Did you test them by putting an old plug in the plug hole, inverting the head & filling with a thin liquid like metho, penetrating oil etc ?
You can sort of test the rings with a wet & dry compression test which is what mechanics did way back then.
More than 10% increase = new rings or rebore.

Also you can run 20w-50 in it and it will slow it down as well.

Quick thought: You did the valves, but did you 'lap them' after ?