Old rubber typewriter feet turn rock hard, or become a sticky mess. They don't make your machine stay at the same place while typing. Keeping these feet will result in the machine sliding all over the place. So to make sure that the machine doesn't move, and/or scratch your typing surface, it is advisable to install new feet. These feet are all printed with Shore A70 TPU. This means that they have the same properties and flexibility as real rubber.

Shore A70 TPU typewriter feet with 100% infil density
Replacement typewriter feet flexibility

Here are a couple examples of the Shore A70 feet. As can be seen, they as good as completely solid, which costs more material and print time, but this means that they are as good as real rubber feet!