The stuff that comes out is not oil but the plasticiser (resin). Very little oil comes out of the ball with it, according to my tests. Ebonite have a new system (Hook-again) which also removes the plasticiser buildup at the surface - they claim (on their site - ebonite.com) that the buildup is caused by track compression from the ball rolling down the lane (I am not convinced that this is the case).
Completely submerging the ball has had no effect on my gear - I don't even bother covering the finger/thumbholes. (disclaimer - I don't use slugs, so don't blame me if they fall out.

Lifters are fine). It may affect very light balls (less dense cores) and will definitely affect older balls with cork-based cores (just in case anyone but me still has one :wink: ).
Use hot water, up to about 70 deg.C and a good detergent - Dawn dishwashing liquid or a good laundry detergent. Leave it soak for 10-15 min, swishing the surface occasionally with a cloth (or, if you are lazy like me just let it soak for an hour or more). Wash off under the hot tap, blot out the holes with paper towels, and let dry.
Most of my gear is polished, and it does not seem to affect the finish.
As far as core separation and cracking goes, try to avoid large (>50deg) temperature changes. Taking a ball from 30 to 70 deg with hot water is a lot safer than pulling one out of the boot in the middle of winter and pouring boiling water on it. If you feel the need to use really hot or boiling water, warm it up to 50-60 deg first.
Oh, and don't use a clothes dryer - the noise upsets the neighbours.