It is the cog spacing that is the problem going from 10 to 9 speed. But since this is Campy, you can simply get an extra 9 speed cog set and mount it on whatever wheelset you want to use with the used bike. The hub is the same for Campy 9 and 10 speed. With a lock ring remover and a chain whip, it is a 5 minute job to switch the cog sets, tops.

Also, if you do not want Branford Bikes to work on your lever, you can order the parts from them and have them ship it to you, and you can rebuild your lever yourself. It is not that hard. Really. Instructions are at www.campyonly.com. I did it when one my rear shifting lever started shifting funny. Turns out that one of the parts was broken (the same part that the guys at campy only replaced) and I was able to use their instructions to take the lever apart, replace the part, and put it back together again. Total cost this way is around $20 to $30 for the parts alone, with a $5 instruction manual to go with it.

Have fun,

BR