If the flush agent on a publish server stops working, then you probably need cq-5.3.0-featurepack-37434. This featurepack is a nice cumulative one - so no painful installation of dependencies (phew)! And it fixes a LOT of bugs mainly around stabilizing the replication services.
We tried installing feature-pack 37434 via CRX package manager but, it broke the instance in that it would just serve up 404 pages.
However, following the below procedure, we were able to install the feature pack.
a. Install, via apache felix webconsole, the following bundles and make sure they are in the active state (start them manually if needed after installation)
b. stop the instance, and drop the FP 37434 v4 into crx-quickstart/repository/install folder
c. start the instance and check that all the bundles are active as expected.
d. We also had to reset the org.apache.sling.jcr.resource.internal.JcrResourceResolverFactoryImpl.xml config to include our resource.resolver.mapping configs.
e. com.day.cq.wcm.cq-wcm-core bundle needed starting.
(NB, don't try accessing the instance too soon - monitor the log file to see when it's finished doing things. Otherwise you still get a 404 response).