10.4.3 server loses contact with AD

Hi all, I have an OS X server version 10.4.3, bound to AD. In my case, binding is not a problem, maintaining it appears to very difficult. So far i tried from 2 different machines (both running 10.4.3 server) with same result: a restart of the server or waiting for 1-2 days will cause the macs to loose connection with AD (lookupd -d; allUsers: displays only local Netinfo users). DNS forward and reverse are good for DCs and OS X servers. I am using a preferred DC on the same subnet as the OS X servers. Anybody can shed some light on this?