That part of mine has been gone for a while now.Someone else had the same thing and just got got it welded.
Upper Left Rear axle trailer/control Arm bracket corroded
Welcome to the club. I had both of mine rot out to the point of being turned down for a sticker. I went and got a piece of 3/16" mild steel and cut and bent the pieces myself large enough to actually enclose the whole original and weld the seams.