Well, for the third time since purchasing this lens (about 18 months ago), I am again faced with the stuck aperture issue. Twice, under warranty, the lens was sent down to the El Segundo repair facility and twice it came back cleaned - only to last about 6 months before the aperture again sticks in the wide open position. So, it looks like it needs to make another trip for another servicing - this time at my cost. Has anyone else experienced repeating problems with this len's aperture blades? I've tried the 'store it vertically' trick, but apparently it made no difference in my case.