Hi!
It's simple! No solvent will!
You have to take it apart because the ballbearings need replacement. If it wasn't for them you could warm the engine and everything would be just fine. Well if its ringed engine you must even then check the ring so that no gummed up castor oil is preventing it from moving freely.
I use aceton when to clean parts after I have disassemble the engine.

Regards!
Jan K