If you start to lose directional control on landing in an MD80 you don't piss about trying to modulate differential reverse thrust that will just get you in more trouble.
You CANCEL reverse immediately to stop the rudder blanking and get on the brakes, reapply reverse carefully if control is established and you need it.
I flew it for four years and we never used that much reverse thrust on a contaminated runway, we all knew that would get you in trouble.