Ercoupe center section repair
Here a few reports on what could go wrong in your planes center section
On the good side, the dreaded Center Section AD requires you to either cut inspection holes on the belly or to disassemble the plane every 3 years or so and inspect with the wings off. If your mechanic has a boroscope, the inspection can be done without taking the wings off, even without inspection panels in the belly.
But best is to take the wings off. That way you can easily see every detail of the center section.
The articles and images here are an example for what to look for and where.
When you find rivets that lost their heads.
If the heads are missing or held on by paint, the rivets most likely are corroded. Don't just replace the rivet, pull a couple on each side and open the skin enough to inspect for corrosion on the skin and structure inside. Missing heads are common on the belly skins along with corrosion inside - especially in the rear spar area.