i test my slide foot, too . . . too much beer on/around our table!!!
i usually wipe off my bowling ball before each shot because i don't want to get oil on my hand. my track is fairly close to my middle finger hole, so i usually have some oil where my "pointer" finger would rest on my ball.
i would think that if you wanted a consistent reaction, you would wipe off your ball . . . otherwise you'll get an oil build-up where your ball is flaring, and it would skid farther down the lane.
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That which does not kill me makes me stronger . . .