Blow By

Rust on the cyl walls, that's an oil burning cause...the rust doesnt just wipe smooth...and if it rusted at the ring..there is now a groove the circumference of the cyl where it rested those years. The surface can leave small pits for blow by

Could have already had many miles on it to boot.
Burning oil under load/throttle. Rings
Burning oil only at start up, seal and guides.