I replaced mine with the T-Bird part # as stated above - my original still looked fine after 30+k miles...changed it with rear tire change.

I honestly can't say I could tell any difference...40k+ later now, still can't. I wouldn't even know what a worn one might do....

Keith
Houston
Ridin'Texas
'04 Speedmaster
AI removed, Pingle, UNI Filter, 1 shim, straight-through slash-cut TORs, Stage 1 DynaJet, 140 mains, 3 turns, 16/42 final drive, 115K
2020 T120 Black