While I don't know for sure, but since I do know that sanding them to get them to react better in the first few games does NOT help, I suspect that they must absorb about 20 - 25 games worth of game oil to kind of "prime the pump". Keep in mind this is only a guess on my part.
I am going through this is with an older but newly drilled Thing Lives right now. AT first, of course, the reaction was nice and smooth, the way I like it. lately it's started to make a left turn (even at 1000 grit matte finish). So I can't use it where I wanted to, might need a weight hole. I'm just entering the 20 game mark. (NOTE: I am NOT saying yours will be flippy.)
So, if I were you I'd do as slashrr69 suggests: only clean off the grunge and dirt that will interfere with the ball's rolling, like belt marks and rough surface dirt.
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"None are so blind as those who will not see."