Looks like those casters on sale were not that good of deal. I think they were $8-10 poly casters rated for 200lbs.
These are on my workbench and as you can see they crumbled, I think they were 5-10 years old. With all the junk on and in my bench it would probably be 400 lbs or maybe more
Now to fix the problem. These were both swivel and roll lock that worked well but I think I want the workbench flat on the floor.
Legs that lower?
Or something else?
I do not have the room under bench bottom to have swing out casters.