It is uncommon to find heads worn to the point where one can snag a fingernail on the surface. Typically the copper-alloy guides will become grooved, but heads remain smooth and intact. What does happen more often on Ampex decks is open head winding. I've had to replace five PB heads over the years, four FWD and one REV. All had Ch. 1 (left track) winding opened. Plenty of good spares exist and Nortronics made good substitutes when necessary. Most difficult spare part to source is plastic control knob, (Function, Volume, Tone, etc.). These D-shaft knobs crack and disintegrate, making repairs difficult.