I have seen a few Tecumseh motors where rings went bad- aluminum and iron blocks so slight maybe it is also leading to your problem.
I had a Briggs with exactly your problem. When running, do u hear a solid metal hitting metal or small ticking noises? On cars and on mine- the noise was solid enough metal hitting metal/piston slap (piston or cylinder worn out - mine cylinder).
Easiest way to confirm, take the cyl head off and push the left and right side of the piston if horizontal to see if there is play. play=wear. Also move piston to BDC and look at the cyl wall if hatchings are gone, potentially cyl too out of round.
If you want to try the easier route first, replace the breather valve\PCV.