Spent too much time configuring port forwarding (RDP) on my (Microtik) RouterBoard 751G-2HnD. The solution, as usual, was buried in a May 2014 forum post. There needs to be TWO (2) NAT rules enabled; i.e. to forward traffic to/fro the router/server.
In this case, 188.8.131.52 and 10.0.0.254 refers to the router’s WAN and LAN IPs respectively, and 10.0.0.243 is the intended recipient of my RDP traffic.
[admin@751g2hnd] > /ip firewall nat print
1 chain=dstnat action=dst-nat to-addresses=10.0.0.243 to-ports=3389 protocol=tcp dst-address=184.108.40.206 dst-port=3389 log=no log-prefix=””
2 chain=srcnat action=src-nat to-addresses=10.0.0.254 to-ports=3389 protocol=tcp dst-address=10.0.0.243 dst-port=3389 log=no log-prefix=””
Many thanks to The Digital Doctor (http://forums.ncix.com/forums/topic.php?id=2662521)!!