Crashes & corrupted imports in Aperture; reinstall?

I have a MacBook Pro that had Aperture preinstalled when I bought it 2 years ago. I recently upgraded to Lion 10.7.5 and Aperture version 3.4.1 after having multiple crashes, but the crashes continued to happen. They happened usually (but not always) when I was using the loupe to inspect images for focus quality. I have repaired the library (after each crash) and also rebuilt the library. I was advised by a tech at the local Apple Store to create a brand new library with all new images and work with it for a while. If it did not crash, that might suggest my old library (or files within the library) was damaged or corrupted in some way. So I created a new library with 4 new projects. Aperture has not yet crashed, but now I am seeing lots of errors on imports from my SD cards. Some files cannot be imported and are put directly into Aperture trash. Others are marked with a badge that indicates the "referenced" originals are missing, but I don't use referenced files, only managed ones. The badges seem to be appearing on different photos each time I launch Aperture. So now I am thinking I should reinstall the software -- but since it came preinstalled, I don't have a CD or App Store purchase. How do I reinstall it?