I previously had AD backup working and my DC cratered. The DC is up and backing up again but AD is not because there is no agent on the rebuilt DC. I have a ticket open, which led me to this.
What I can’t figure out is how to download the AD agent again. It looks like the way it’s done is as part of the AD backup setup in the first place. All of the connection info is still in place. Is there a way to re-load the agent, or does the setup have to be done from scratch (as in Add → Active Directory)?

