Think about it, when you're wiping.....the oil isn't really coming up, you're just smearing. I leave it be. I'll agree it's a force of habig for most bowlers. For instance, I'll swipe my foot on the approach a few times to make sure I get a good feel and nothing is on my sole. Even when there's no problem with the approaches I still do it. Force of habit.
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-DP3
Respect the Game