If it's truly a mono sample converted to stereo when exported, it should be the same audio on the left and right. In Logic 9 go to Window>Mixer and on the channel that has the audio, push the "stereo" button at the bottom of the strip. This will convert that channel to mono. See the image.

This will sum the left and right audio resulting in a louder sample, just turn it down some.
If the audio has a stereo image with different audio on each side, this method will not work as expected and will require a different approach.
http://www.logicprohelp.com/forum/viewtopic.php?f=1&t=98428There is even yet another approach when using MPC as a plugin, which is how I work. It involves creating a Bus for each stereo image that you want to be split. For instance, I have a kick panned hard left and a snare panned hard right. I create a "Bus 1 Left" and "Bus 1 Right" and send that stereo signal to "Bus 1", but have separate channel strips for snare and kick. The image below is from Logic X so the "Stereo" buttons are slightly higher in the channel strip, but same concept.

There may be other ways to handle it, but this is how I do it.