The only 3D Printed part we ever had an issue with was a PLA "spindle" we made for the elastic bands on the shooter of our 2014 robot (it prevented the bands from rubbing against the sharp 90 degree corners of the 1"x1" aluminum tube they attached to).
Needless to say our shooter was WAY over-tensioned for what it needed to be, so the part kept being crushed under the force of the elastic bands. After replacing it twice we finally just printed one at 100% infill and never had another problem with it (we had one of the free Cube printers, so our only options were basically: "no fill", "some fill", and "ALL THE FILL").
As long as the part itself is not too small for the application, when in doubt, add more infill.
