FIX THIS IMMEDIATELY,
Think about it. You're door could literally come unlatched in a crash, your SEAT BELT is attached to the door. You end up as road kill because of some weak metal...
The problem lies in extremely weak sheet metal with no bracing to support. This is how door sag in all B13's occurs IMO.
I edited the pic real quick to give you an idea of what to do.
Black - Amount of actual car sheet metal removed. Once removed get latch out of ****ty tin foil excuse of sheet metal. Tack this in with a mig a first.
White - These will be holes in existing sheet metal. These are intended as reinforcement points for above stated tin foil. Start in the middle of the coin (you'd be hitting the 1/4 plate) and circle your way out to the existing sheet.
Green - Estimated extending area of 1/4 plate that has been put in.
1. Completely remove affected sheet metal in a patch similar to picture.
2. Weld 1/4 in. sheet steel in.
3. Reinforce as best you can.
4. Prime or por-15 it.
5. Reattach latch into threaded holes made with thread borer.
6. Solid latches the way they shoulda come from the factory.
This is just a guess how to fix it. I haven't messed with mine cause they don't sag soo... follow at your own risk.