I had that same problem with a Gen 2 I had about 15 years ago - seems to be a more common problem in the Gen 2 than Gen 3 and other Performers (which is one of the reasons Gen 2 is my least favorite design).
It’ll take some Creativity to get a tubing match that the caster fits snugly in and won’t rust away in the future. I wasn’t able to get a solid, permanent fix, despite the many hours I tried......so when we sold the house I left the grill for the new owner.