Forum Moderators: travelin cat
As I always put in both new modules at the same time to make sure all of the specs match, I have never encountered this before, however I found a reference to this on Apple's site:
According to the person installing the new memory it is the one on the right when viewing the mac from the bottom. According to the Apple tech in the thread, it will not matter which side you put it in so you could give the right a try, boot up the Mac and go to "About This Mac" in the Apple menu, click on "More Info..." to see which bank has the larger memory. Then make any changes you feel comfortable with.