I work at an airconditioning place, you can get them rebuilt, but sometimes it can be more cost effective to replace the pump with a new one.

Second hand, you're likely to have similar problems down the track. If the second hand pump has been sitting around for a while the seals have more than likely dried out and as soon as they turn over the first time, they will get damaged by the lack of lubrication, and start leaking.

I can find out a price tomorrow, or if you want I can give you our work number and the name of one of our spare parts interpreters.

Cheers
MCL