Get the service manual. It shows how to disassemble the radio. The BNC connector looks very much like the standard one. It should not be much of a challenge to exchange it as DIY, especially looking at the labor rate.
And be happy you got the BNC connector, many HTs have SMA now.
You know, I think I will do that. The worst pat of the job is to de-solder part...http://www.scribd.com/doc/37392767/Icom-IC-Z1-Service-Manual