Be careful scrubbing around inside the frame with a toothbrush, there's a tiny little bronze-colored leaf spring that's easily bent, which results in the infamous "4506 trigger click". The pistol will still function, but it's annoying as hell.
I had the click, and after some research, just bent it back straight, and it worked. But I've read that this fix often doesn't last, and it will eventually need replacement.
I got a spare spring sent to me free from S&W's CS a couple years ago, but don't know if they still have them on hand. Last I checked, Brownells sold the spring and tiny rivet for $10-15.
Anyway, you got a killer deal on a spectacular pistol !!