Resolution:
We recommend using RVRD to route traffic over a WAN instead of using multicast.

Some of the reasons for not using multicast over the WAN are timing issues as a result of network delays, and routers dropping UDP packets for TCP packets during high utilisation of the network.    

Timing issues can arise from delays in delivery of packets across a WAN.  RVRD uses TCP, which is more robust when dealing with network delays across a WAN.  

Also, some routers when loaded will start dropping UDP packets in favour of TCP traffic.  This is why we recommend using RVRDs to bridge multicast traffic over a WAN.  

Please note, however, that some WAN configurations may have the backbone to handle the load and make timely deliveries to negate the issues.