avoid Rover 75 + mg ZT with 1.8 petrol engines, it’s not a case of if but when they have a head gasket failure! As mentioned above the diesel is the best engine but the 2.0 and 2.5 v6 variants are pretty good (if a little thirsty).
I’ve had a diesel 75 tourer for the last 6 years and love it. It’s comfy on long journeys has lots of toys and is fairly economical (42mpg urban/55mpg motorway) and with the back seats down I can put my DH bike in without removing wheels.
all the variants of this car have some little problems but they were vastly under rated and maybe thought a little grey in a pipe n slippers way when they were being produced.
Most of my repair info comes from here –> http://forums.mg-rover.org/forumdisplay.php?f=90