It took some fantastic pictures - the Sonnar 50/1.5 is a killer lens. Mine had severe balsam separation that had people running for the hills, but it worked great - even in direct sunlight, and produced nice color photos, too. Contax lenses are hard to come by, and of course on eBay many are extortionately priced. Voigtländer (Cosina) made some good lenses, and Russian KIEV mount lenses are good, too - especially the Jupiter-12 35/2.8. You could also try Nikon rangefinder mount (S-mount) lenses, as long as they're wider than 50mm.
Check to make sure that Bulb works properly, and that 1/1250 actually opens - I believe those are the two speeds that can give trouble. Also see if you can run a test film through it, and check the fast speeds to make sure they're exposing the film properly.