Oil control rings losing their ability to seal, leading to blowby as you suspect.
These engine's rear main seals are robust, so it's something else that is likely making them go bad.
Damage to the crank sealing surface may also be the culprit.
These engine's rear main seals are robust, so it's something else that is likely making them go bad.
Damage to the crank sealing surface may also be the culprit.