Replication Issues

I've got a bit of a doozie I've been researching for a little while now that's really irking me. Right now I'm working with a domain with 3 Domain Controllers, one just added today. Two of the domain controllers are in one location (SERVER1 & SERVER3) while the other is across town in another office (SERVER2), connected by a T1 line. That DC used to be a DC on a different domain but was demoted, joined to the new domain and promoted to a DC to handle the traffic at that office. I noticed a problem right away in that changes made to Active Directory on SERVER2 were not replicating to SERVER1. Through some research and trying a few different things, I was starting to think it had something to do with the outbound replication traffic from SERVER2 not making it across the T1 to SERVER1 for some reason and was about to investigate that.

However, when I installed the new DC today, SERVER3, the same problem occurred even though SERVER3 is within the same LAN as SERVER1. I've tried making SERVER2&3 Global Catalog servers and taking that role away from SERVER1. I've also tried transferring all the Operations Master roles to SERVER3 and SERVER1 drops the roles but doesn't pick up on the fact that SERVER3 now had them. So basically SERVER2 & SERVER3, the newest DCs, will pull any AD changes from SERVER1, the original server on the network, but none of the servers will pull changes made on either SERVER2 or SERVER3. Also, replication can not be done manually from Sites & Services. I get an "RPC service unavailable" or a "Domain Naming service" error. (I can get the full error messages if needed)

Each server is running DNS with host entries for each server clearly in each. Also, there is no network connection problem between the servers. I can see & browse them from each other with no problem.

The main problem with this is I need to take SERVER1 out of commission & totally rebuild it, with SERVER3 taking over as the main DC. With changes made to SERVER3 not being pulled by the other servers, I'm afraid of what will happen when I take out SERVER1, the only DC capable of making global changes.

I'd appreciate any help anybody can offer. I've been battling with this for about a month now.

 

Is this a dedicated Private T1 or a VPN over a T1?

What are the subnets and masks?

How is DNS configured?

Anything significant in the error logs?