I bought an old LeMond Buenos Aires in mint condition a few years ago that was a replacement for an Alp d'Huez I rode for 20 years then sold. The BA came with 10 spd Sram Apex shifters and deraiileurs. I've put about 1k miles on it and I just don't like the Sram doubletap shift action, so I bought some lightly used Tiagra 10 speed shifters to put on. So now I need some derailleurs and my question is: should I go with a used 105 10 speed derailleur or just get a new Tiagra one? I'm worried a used derailleur might already have significant mileage and wear on it. I am quite familiar with what a worn derailleur is like since I replaced a Shimano 600 that was completely shot, last year.