RE: OS 55AX
The bronze bushes (bearings) are porous. They absorb and hold oil. During any cleaning of the internal components with a solvent, you need to make sure any oil leached out is replaced.
Leaving a solvent to soak parts, it is possible to disolve and leach out all the oil. The part then needs to be soaked in oil (preferably at a warm temperature) to replenish the lost oil.
An engine started with a lack of oil in the bearings will cause a lack of lubrication until the bearing soaks up enough oil (from the incoming fuel charge) to become "full".
I've always thought the above was correct but I'm happy to be corrected if it's wrong.