the condition is that the replacement ECU must be similar or newer than yours,(e.g. if yours is MSB101184 dont put MSB101183, put MSB101184, MSB101330...or the NNN000120/NNN500020) then put in the new(used) one, syncronize it with the immobiliser(with tester) after that u can send it to be chipped/remapped cos they will keep the settings...or you can send the original one to be chipped..... the NNN types are better cos they are flashable, the chip is not soldered into the circuit. Be aware that manual ECU's are not compatible with auto's and vice-versa. Here is a list for Discovery in chronological order if u are interested:
MSB101183 1 ELECTRONIC CONTROL UNIT ENGINE, MANUAL TRANSMISSION
MSB101184 1 ELECTRONIC CONTROL UNIT ENGINE, MANUAL TRANSMISSION
MSB101330 1 ELECTRONIC CONTROL UNIT ENGINE, MANUAL TRANSMISSION
NNN000120 1 ELECTRONIC CONTROL UNIT ENGINE, MANUAL TRANSMISSION
NNN500020 1 ELECTRONIC CONTROL UNIT ENGINE, COOLED EGR, CHECK FOR SERVICE EXCHANGE VERSION, MANUAL TRANSMISSION
LR006328 1 ELECTRONIC CONTROL UNIT ENGINE, EXCHANGE PART (RE-MANUFACTURED), COOLED EGR, MANUAL TRANSMISSION
NNN500250 1 ELECTRONIC CONTROL UNIT ENGINE, NON COOLED EGR, MANUAL TRANSMISSION
MSB101192 1 ELECTRONIC CONTROL UNIT ENGINE, AUTOMATIC TRANSMISSION, '(+)"EUROPE/J"'
MSB101193 1 ELECTRONIC CONTROL UNIT ENGINE, AUTOMATIC TRANSMISSION, '(+)"EUROPE/J"'
MSB101340 1 ELECTRONIC CONTROL UNIT ENGINE, AUTOMATIC TRANSMISSION, '(+)"EUROPE/J"'
NNN000130_USE 1 ELECTRONIC CONTROL UNIT ENGINE, AUTOMATIC TRANSMISSION, '(+)"EUROPE/J"'
NNN500030 1 ELECTRONIC CONTROL UNIT ENGINE, AUTOMATIC TRANSMISSION, '(+)"EUROPE/J"'
LR006301 1 ELECTRONIC CONTROL UNIT ENGINE, EXCHANGE PART (RE-MANUFACTURED), REAR, AUTOMATIC TRANSMISSION, '(+)"EUROPE/J"'
MSB101260 1 ELECTRONIC CONTROL UNIT ENGINE, (AUTOMATIC TRANSMISSION, '(-)"J"' OR AUTOMATIC TRANSMISSION, '(-)"EUROPE"')
MSB101261 1 ELECTRONIC CONTROL UNIT ENGINE, (AUTOMATIC TRANSMISSION, '(-)"J"' OR AUTOMATIC TRANSMISSION, '(-)"EUROPE"')
MSB101350 1 ELECTRONIC CONTROL UNIT ENGINE, (AUTOMATIC TRANSMISSION, '(-)"J"' OR AUTOMATIC TRANSMISSION, '(-)"EUROPE"')
MSB000130 1 ELECTRONIC CONTROL UNIT ENGINE, (AUTOMATIC TRANSMISSION, '(-)"J"' OR AUTOMATIC TRANSMISSION, '(-)"EUROPE"')