In order for the hole to be enlarged something must have been moving inside it to wear away the surface.

Using a ball link normally would have the screw tightened securely so that any rotation occurs inside the ball link between the ball and its socket. The only way for the phenolic horn to have become worn is if the screw attaching the ball link to have come loose.

Maintenance on these planes is very important, periodic checking/tightening of screws and other fasteners helps to protect your investment.

Just an FYI, all new airplane designs from Wild Hare will be using double-truss control horns with ball links, but even with this design if the screw is not tight the inner surface can get worn.

TF