Older wall hung toilet problem

I've inherited a beautiful home with a lot of problems. The home was remodeled in the mid 70s with a wall hung toilet in the master bath. I had a huge water bill the first month I took it over and found the toilet was the culprit as it "runs" constantly. My son, the previous tenant, says the plumber he hired bought a kit and replaced much of the inner workings and it apparently worked for a time, was replaced a second time, and continues to have the same problem.

I can't find a manufacturer's name on it and my son says the plumber had to find the original plumber to get the name but all that paper work is lost.

So... I guess I have to replace it? If so, what would be a good replacement? If not, what can I do to fix it? I don't have a lot of money.

A picture of the old water closet would be a help. Take a picture of the overall water closet and then focus on where it is attached to the wall. These two pictures will be a huge help.

There is a couple styles out there. If it has a tank Crane still makes one and so does Elger. Also how many bolts hold it to the wall. And does it sit on the floor and discharge in to he wall, or does it just hang on the wall?

also take a pic inside the tank, alot of toilet tank parts can be replaced with basic store bought parts, get the good parts though and rebuild the whole thing, not just most parts, a good thorough rebuild of all moving parts will save alot of money, if the china is good why replace the whole toilet?

Here are photos of the toilet. Thanks for taking the time to help.

Looks like a Case 3000.
See this thread
https://terrylove.com/forums/showthread.php?t=24538&highlight=case+3000
or this for parts
https://terrylove.com/forums/showthread.php?t=22500&highlight=case+3000