Leaking wall mounted American Standard toilet

This toilet is approximately 40-45 years old. Wall mounted, not used as much as others in our home. Appearance wise it still looks great. What would you suggest we do? It is leaking on to the ceiling of our downstairs room

Make sure there are no leaks from the tank fittings first.

If you are sure that the toilet itself is not leaking, then you would be looking at the seal most likely.

You wil have to pull the bowl from the wall, and replace the seal.
Zurn and some others have a rubber foam seal for wall hungs, and there are a few "wall mounted" rated wax type seals too.

When you reassemble, you tighten three nuts, and hand tight the fourth.
Think tricycle. Only thee wheels touch, it's the same with a wall hung, you will never get all four points to touch, if you tighten the forth, it will crack the bowl.