Been taking on some water the past year, I figured I would remove my drain plug plate (the whole assembly) and low and behold.... the thing is barely on. So, 2 of 3 screws tightened up very securely while 1 screw goes on so so, then just spins in place. Should I put some 4200 in that hole and re-drill it or something? The silicon gasket was fine behind the plate, just not 100% certain how to go about fixing this.

I would use epoxy to fill the hole and re drill.