OD-AD Integration, adding a Replica

Our institution has two XServes running Server 10.5.8. We have successfully followed the AD-OD Sandbox guide. Our Macs are getting MCX from OD and the user accounts are managed in AD. All good. We have a spare XServe doing very little, so I decided to create an OD Replica. It seemed to go OK, but Kerberos on it changes between Running and Stopped. The processor is running higher. In the kadmin.log I see:

Jun 10 11:48:10 server.example kadmind[12170](Error): No such file or directory while initializing, aborting

And in the kdc.log I see:

krb5kdc: No such file or directory – while initializing database for realm SERVER.EXAMPLE

These entries are repeated endlessly several times a minute. In both cases, where I’ve written server.example it’s actually got the host name of the OD Master. Actually our Kerberos Realm is from the AD. On the OD Master, in Server Admin, it displays itself as the Kerberos Realm, but running the command sudo klist -kt it’s clearly using the AD. Whereas on my Replica, running the same command, it’s using itself, which doesn’t seem right to me.

I’ll put my hands up, I don’t know a great deal about this. It made sense to me to build some redundancy to our OD. Should I pursue this and is there an easy config change? Or am I doing something pointless that’s destined to be ropey?