I'm cross-posting this from another post as I feel the information is important.
This month's Good Sam magazine had a great article on hitches. One of the things they talked about was age of hitches and maintenance. They indicated that if you use a hitch across multiple vehicles and it's getting older to inspect it very carefully.
What you are looking for is ovaling in the receiving hole for the spring bars. If the holes have ovaled the hitch should be replaced. It can cause your spring bars to drop out of the hole and drag along the road. I've actually seen this happen. Fortunately the people were in the campground when it dropped and not on the highway. If it happens on the highway it will cause uneven leveling (is that an oxymoron?) and could cause dangerous sway control.
The other thing to check are the welds. If there are any cracks you need to replace the hitch. I do not believe it is legal to repair welds on a hitch.