Are you referring to the current 300LIS f4 or the previous non-IS version? Both are optically very good lenses. The non-IS is probably at least 20 years old and more difficult to hand hold for steady images. Don't know if Canon still provides service for it. The current IS version solves hand holding with two stops of effective stabilization. It uses an older technology IS that gives an audible clunk noise when IS starts up but that's normal.
1DX MK II, 5D MKIV x2, 24L II, 35L II, 50L, 85LIS, 100LIS Macro, 135L, 16-35LIS, 24-105LIS II, 70-200LIS, 100-400LIS II