Joined: Jan 2008
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From: Hint: check out my BF name
Bikes: 2016 Parlee Altum, 2013 Cannondale Super Six Evo Hi Mod Di2 only, 2011 Cannondale Super Six, Dura Ace 7800, 2007 Cannondale System Six Dura Ace 7800, 1992 Bridgestone RB-1, MB-2, MB-3, MB-5
Another possibility to consider, aside from different tubes or tires:
Do you check the rim on both sides to make sure the tube is set fully inside the tire?
Is the source of leakage near the pin? Could you possibly be causing a small leak by the way in which you inflate the tires?
Consider checking for the source of the small leak in each tube to assess whether there is a pattern; if so, you might then be able to identify the source of the slow leak.
Good luck. It is maddening!!