Active Directory : Replication Issue - "Disconnected" sub-domain from the Forest

Question

Hello everyone,
I'm managing a multi-domain forest (with 7 sub-domain).  All are working fine except for one.  Throught repadmin (Repadmin /replsum /bysrc /bydest /sort:delta), I noticed I got both domain controllers of a subdomain (there are only 2 DCs in that
subdomain), who hadn't replicated with the rest of the forest for more than 60 days.
According to my research, it's usually recommended to Depromote and repromote the problematic DC to avoid the issue of lingering objects.  In this case, it's both DC of a sub-domain.  Of course, on the others DCs in the forest, I got the event
ID 2012 "it has been too long since this machine last replicated with the named source machine....". 
 HKLM\System\CurrentControlSet\Services\NTDS\Parameters\Allow Replication With Divergent and Corrupt Partner
to a value of 1. 
As I understand it, this may cause lingering objects to appear (they can be removed with repadmin /removelingeringobjects command with the DSA GUID, naming context, etc..).  So far, I haven't used that registry key yet because of the associated risks.
I didn't noticed any other issue so far.  Users in the problematic sub-domain are fine, and the problematic sub-domain seems to be able to pull replication data from the others DCs in the forests. (at least, I'm not getting any error in the A.D. Sites
and Services)
I added two new DCs for the affected sub-domains, so the number of DCs for that domain went from 2 to 4 DCs.  The two old DCs that hadn't replicated for 60 days are windows Server 2003 and the two new DCs are Server 2008 R2. 
Unfortunately (and I was half expecting this, but did it anyway since I must eventually replace the old DCs), that didn't solve my issue, since the rest of the forest "doesn't see" the two new DCs of the sub-domain.  By that, I mean that I
cannot add an Active Directory Domain Services Connection in Sites & Services console (from a DC in another domain of the forest or even the root domain).  I see all the DCs, including the two old DCs that are server 2003, but not the new ones. 
I believe it's because the others DCs doesn't pull/replicate the information from the old DCs anymore, so they aren't "aware" of the two new DCs for that problematic sub-domain.
I was wondering what is the best course of action. Is it worthwhilte to use the registry key force replication with the old DCs ?  (and hopefully, the new DCs will get their AD Services connection/replication vector created, so I can depromote
the old DCs.
Since the Old DCs from the problematic sub-domain seems to be able to pull the replication from the rest of the forest, does the risk of Lingering object isn't that great ?
Or is it too risky and I must create a new sub-domain and migrate one way or another the users ? (which would be time-consuming)
Thanks in advance,
Adam

Answer 1

Thanks for the reply.  One of the link had another link to a good article about the use of repadmin :
So, I ran the command "repadmin /removinglingerobjects " on one of the problematic DCs ().
For clarity purpose, let's say I used the domain :
domain = main domain
subdomain = the domain whose DC are problematic (all of them).
AnotherSubDomain = Just another subdomain I used as a "reference" DC to cleanup the appropriate partition.
Command (the DSA guid is from a DC "clean" in another domain)
repadmin /removelingeringobjects adrec01.mysubdomain.domain.ca C4081E00-921A-480D-9FDE-C4C34F96E7AC dc=ANOTHERsubdomain,dc=domain,dc=ca /advisory_mode
I got the following message in the event viewer :
Active Directory Domain Services has completed the verification of lingering objects on the local domain controller in advisory mode. All objects on this domain controller have had their existence verified on the following source domain controller.
Source domain controller:
c4081e00-921a-480d-9fde-c4c34f96e7ac._msdcs.mydomain.ca
Number of objects examined and verified:
0
Objects that have been deleted and garbage collected on the source domain controller yet still exist on this domain controller have been listed in past event log entries. To permanently delete the lingering objects, restart this procedure without using the
advisory mode option.
How should I interpret the message "number of objects examined and verified 0".  Does it mean it just didn't find any object to compare ? (which would be odd IMHO)  Or there is another problem ?
Thanks in advance,
Adam