Hey guys I recently purchased a s&w 6904. somehow the rear sight came lose and it wont stay tight. I am not sure how it happened but I was going to order a pair of night sights. What I realized is under the rear sight the small oval plate that keeps the spring compressed is missing. Can I put on new sights without that plate? I ask because I cant find a replacement anywhere.

To my knowledge, none of the 9mm 3rd gens use the oval plates - the springs are compressed by the bottom of the rear sight itself.

You can stake some divots in the dovetail slot to tighten that up. I had this problem with hard chromed Browning HP and staked up the inside of the dovetails to keep the sights from shifting.
And no, there's nothing under the sight on the Novack 3rd gen rear, only the springs and plungers. No plate.