I am either going to buy a 99 or 990 whats the major advantages to each version? Are there any things I need to look for? I have found a 990 with the silver slide for $500 used, but it has about 7-8 flecks of rust on the slide, (from the guys not wiping it down after being handled, i think) is this a good deal or a rip off? thanks for all the info.