Non-reactive Urethane balls can absorb oil (more slowly of course). However, that doesn't have as much effect on their reaction. With urethane balls, surface dominates the reaction. If you have a shiny hard urethane (pink hammer), it would tend to hook a wee bit more as the surface wears and tracks up. Theoretically, a pink hammer could be resurfaced and shined again, but I doubt it would ever be as "straight" as the original out-of-box condition. I'e heard horror stories about attempts to restore really hard shiny urethane balls (Black Angle, Pink Hammer, Burgundy Pin Breaker, etc.) The original Black Hammer had a cover that was very easy to shine or dull as required.
With a dull rough surface urethane ball, the oil can be cleaned and the cover restored to it's original texture/grit as often as needed until the ball gets too small to use.
