This is a known issue with some fox forks made in the 2010-2012 range. Fox's fix for this problem is to replace the foam ring on the air piston with a rubber oil scraper but unfortunately not all of the forks air pistons had a foam ring to replace. In that case you can replace the air seal and see if it helps but unfortunately there is no guarantee. For more information google “fox oil migration” or read through this thread http://forums.mtbr.com/shocks-suspension/bath-oil-migrating-top-air-piston-734912.html Good luck
